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 $226.77   8.693%   $246.4831   $246.48   $246.50   $246.50  
  Purchase #2 $110.93   12.275%   $124.5467   $124.55   $124.55   $124.50  
  Purchase #3 $173.73   4.395%   $181.3654   $181.37   $181.35   $181.40  
  Purchase #4 $119.89   13.303%   $135.839   $135.84   $135.85   $135.80  
  Purchase #5 $150.51   9.406%   $164.667   $164.67   $164.65   $164.70  
  Purchase #6 $120.69   13.267%   $136.7019   $136.70   $136.70   $136.70  
  Purchase #7 $193.31   12.468%   $217.4119   $217.41   $217.40   $217.40  
  7 purchase totals = $1,095.83       $1,207.0150   $1,207.02   $1,207.00   $1,207.00