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 $95.49   3.177%   $98.5237   $98.52   $98.50   $98.50  
  Purchase #2 $90.69   12.574%   $102.0934   $102.09   $102.10   $102.10  
  Purchase #3 $91.76   11.435%   $102.2528   $102.25   $102.25   $102.30  
  Purchase #4 $220.53   5.553%   $232.776   $232.78   $232.80   $232.80  
  Purchase #5 $103.30   3.762%   $107.1861   $107.19   $107.20   $107.20  
  Purchase #6 $161.51   6.136%   $171.4203   $171.42   $171.40   $171.40  
  Purchase #7 $142.34   6.872%   $152.1216   $152.12   $152.10   $152.10  
  7 purchase totals = $905.62       $966.3739   $966.37   $966.35   $966.40