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 $66.29   12.754%   $74.7446   $74.74   $74.75   $74.70  
  Purchase #2 $152.38   9.419%   $166.7327   $166.73   $166.75   $166.70  
  Purchase #3 $57.58   4.175%   $59.984   $59.98   $60.00   $60.00  
  Purchase #4 $48.34   11.830%   $54.0586   $54.06   $54.05   $54.10  
  Purchase #5 $195.54   3.585%   $202.5501   $202.55   $202.55   $202.60  
  Purchase #6 $42.63   13.212%   $48.2623   $48.26   $48.25   $48.30  
  Purchase #7 $123.32   9.774%   $135.3733   $135.37   $135.35   $135.40  
  7 purchase totals = $686.08       $741.7056   $741.69   $741.70   $741.80