Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $250.62   5.736%   $264.9956   $265.00   $265.00   $265.00  
  Purchase #2 $122.35   7.625%   $131.6792   $131.68   $131.70   $131.70  
  Purchase #3 $160.51   3.685%   $166.4248   $166.42   $166.40   $166.40  
  Purchase #4 $169.76   11.744%   $189.6966   $189.70   $189.70   $189.70  
  Purchase #5 $196.76   13.792%   $223.8971   $223.90   $223.90   $223.90  
  Purchase #6 $200.26   5.793%   $211.8611   $211.86   $211.85   $211.90  
  Purchase #7 $171.93   6.452%   $183.0229   $183.02   $183.00   $183.00  
  7 purchase totals = $1,272.19       $1,371.5773   $1,371.58   $1,371.55   $1,371.60