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 $177.32   13.756%   $201.7121   $201.71   $201.70   $201.70  
  Purchase #2 $245.48   12.269%   $275.5979   $275.60   $275.60   $275.60  
  Purchase #3 $65.32   12.619%   $73.5627   $73.56   $73.55   $73.60  
  Purchase #4 $180.88   12.222%   $202.9872   $202.99   $203.00   $203.00  
  Purchase #5 $96.99   10.618%   $107.2884   $107.29   $107.30   $107.30  
  Purchase #6 $12.30   8.821%   $13.385   $13.39   $13.40   $13.40  
  Purchase #7 $65.61   9.702%   $71.9755   $71.98   $72.00   $72.00  
  7 purchase totals = $843.90       $946.5088   $946.52   $946.55   $946.60