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 $42.94   11.127%   $47.7179   $47.72   $47.70   $47.70  
  Purchase #2 $104.87   11.261%   $116.6794   $116.68   $116.70   $116.70  
  Purchase #3 $125.27   11.301%   $139.4268   $139.43   $139.45   $139.40  
  Purchase #4 $159.54   8.720%   $173.4519   $173.45   $173.45   $173.50  
  Purchase #5 $13.25   10.211%   $14.603   $14.60   $14.60   $14.60  
  Purchase #6 $235.80   9.219%   $257.5384   $257.54   $257.55   $257.50  
  Purchase #7 $191.66   10.374%   $211.5428   $211.54   $211.55   $211.50  
  7 purchase totals = $873.33       $960.9602   $960.96   $961.00   $960.90