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 $97.47   13.318%   $110.4511   $110.45   $110.45   $110.50  
  Purchase #2 $244.90   13.362%   $277.6235   $277.62   $277.60   $277.60  
  Purchase #3 $30.54   12.834%   $34.4595   $34.46   $34.45   $34.50  
  Purchase #4 $166.31   8.860%   $181.0451   $181.05   $181.05   $181.00  
  Purchase #5 $94.72   10.654%   $104.8115   $104.81   $104.80   $104.80  
  Purchase #6 $131.78   3.165%   $135.9508   $135.95   $135.95   $136.00  
  Purchase #7 $115.25   10.657%   $127.5322   $127.53   $127.55   $127.50  
  7 purchase totals = $880.97       $971.8737   $971.87   $971.85   $971.90