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 $48.27   6.308%   $51.3149   $51.31   $51.30   $51.30  
  Purchase #2 $47.96   3.285%   $49.5355   $49.54   $49.55   $49.50  
  Purchase #3 $104.48   4.122%   $108.7867   $108.79   $108.80   $108.80  
  Purchase #4 $191.37   4.862%   $200.6744   $200.67   $200.65   $200.70  
  Purchase #5 $194.52   3.357%   $201.05   $201.05   $201.05   $201.10  
  Purchase #6 $115.78   12.369%   $130.1008   $130.10   $130.10   $130.10  
  Purchase #7 $19.48   5.312%   $20.5148   $20.51   $20.50   $20.50  
  7 purchase totals = $721.86       $761.9771   $761.97   $761.95   $762.00