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 $41.54   10.598%   $45.9424   $45.94   $45.95   $45.90  
  Purchase #2 $177.92   9.424%   $194.6872   $194.69   $194.70   $194.70  
  Purchase #3 $99.81   12.812%   $112.5977   $112.60   $112.60   $112.60  
  Purchase #4 $107.53   13.650%   $122.2078   $122.21   $122.20   $122.20  
  Purchase #5 $213.93   3.150%   $220.6688   $220.67   $220.65   $220.70  
  Purchase #6 $161.61   10.399%   $178.4158   $178.42   $178.40   $178.40  
  Purchase #7 $153.65   7.504%   $165.1799   $165.18   $165.20   $165.20  
  7 purchase totals = $955.99       $1,039.6996   $1,039.71   $1,039.70   $1,039.70