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 $87.28   11.132%   $96.996   $97.00   $97.00   $97.00  
  Purchase #2 $10.98   6.310%   $11.6728   $11.67   $11.65   $11.70  
  Purchase #3 $162.53   12.793%   $183.3225   $183.32   $183.30   $183.30  
  Purchase #4 $60.48   3.486%   $62.5883   $62.59   $62.60   $62.60  
  Purchase #5 $172.27   10.664%   $190.6409   $190.64   $190.65   $190.60  
  Purchase #6 $243.38   6.238%   $258.562   $258.56   $258.55   $258.60  
  Purchase #7 $9.51   10.247%   $10.4845   $10.48   $10.50   $10.50  
  7 purchase totals = $746.43       $814.2670   $814.26   $814.25   $814.30