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 $213.49   5.738%   $225.7401   $225.74   $225.75   $225.70  
  Purchase #2 $130.36   4.452%   $136.1636   $136.16   $136.15   $136.20  
  Purchase #3 $114.74   4.362%   $119.745   $119.75   $119.75   $119.70  
  Purchase #4 $22.68   13.835%   $25.8178   $25.82   $25.80   $25.80  
  Purchase #5 $116.66   4.732%   $122.1804   $122.18   $122.20   $122.20  
  Purchase #6 $99.48   7.799%   $107.2384   $107.24   $107.25   $107.20  
  Purchase #7 $220.89   11.620%   $246.5574   $246.56   $246.55   $246.60  
  7 purchase totals = $918.30       $983.4427   $983.45   $983.45   $983.40