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 $64.92   6.717%   $69.2807   $69.28   $69.30   $69.30  
  Purchase #2 $60.95   9.621%   $66.814   $66.81   $66.80   $66.80  
  Purchase #3 $55.55   4.847%   $58.2425   $58.24   $58.25   $58.20  
  Purchase #4 $132.74   8.302%   $143.7601   $143.76   $143.75   $143.80  
  Purchase #5 $142.95   8.485%   $155.0793   $155.08   $155.10   $155.10  
  Purchase #6 $159.74   9.275%   $174.5559   $174.56   $174.55   $174.60  
  Purchase #7 $104.81   7.622%   $112.7986   $112.80   $112.80   $112.80  
  7 purchase totals = $721.66       $780.5311   $780.53   $780.55   $780.60