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 $108.78   8.560%   $118.0916   $118.09   $118.10   $118.10  
  Purchase #2 $225.57   5.837%   $238.7365   $238.74   $238.75   $238.70  
  Purchase #3 $22.59   6.625%   $24.0866   $24.09   $24.10   $24.10  
  Purchase #4 $150.39   6.653%   $160.3954   $160.40   $160.40   $160.40  
  Purchase #5 $107.29   9.651%   $117.6446   $117.64   $117.65   $117.60  
  Purchase #6 $95.43   7.311%   $102.4069   $102.41   $102.40   $102.40  
  Purchase #7 $185.96   4.648%   $194.6034   $194.60   $194.60   $194.60  
  7 purchase totals = $896.01       $955.9650   $955.97   $956.00   $955.90