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 $165.53   6.672%   $176.5742   $176.57   $176.55   $176.60  
  Purchase #2 $46.86   9.646%   $51.3801   $51.38   $51.40   $51.40  
  Purchase #3 $136.61   8.809%   $148.644   $148.64   $148.65   $148.60  
  Purchase #4 $12.63   10.483%   $13.954   $13.95   $13.95   $14.00  
  Purchase #5 $243.73   6.733%   $260.1403   $260.14   $260.15   $260.10  
  Purchase #6 $249.82   12.494%   $281.0325   $281.03   $281.05   $281.00  
  Purchase #7 $113.48   7.631%   $122.1397   $122.14   $122.15   $122.10  
  7 purchase totals = $968.66       $1,053.8648   $1,053.85   $1,053.90   $1,053.80