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 $210.46   8.411%   $228.1618   $228.16   $228.15   $228.20  
  Purchase #2 $150.41   5.835%   $159.1864   $159.19   $159.20   $159.20  
  Purchase #3 $45.42   12.669%   $51.1743   $51.17   $51.15   $51.20  
  Purchase #4 $240.77   13.529%   $273.3438   $273.34   $273.35   $273.30  
  Purchase #5 $144.65   6.311%   $153.7789   $153.78   $153.80   $153.80  
  Purchase #6 $63.87   5.734%   $67.5323   $67.53   $67.55   $67.50  
  Purchase #7 $84.35   11.174%   $93.7753   $93.78   $93.80   $93.80  
  7 purchase totals = $939.93       $1,026.9528   $1,026.95   $1,027.00   $1,027.00