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 $225.71   10.763%   $250.0032   $250.00   $250.00   $250.00  
  Purchase #2 $64.71   12.546%   $72.8285   $72.83   $72.85   $72.80  
  Purchase #3 $249.38   9.448%   $272.9414   $272.94   $272.95   $272.90  
  Purchase #4 $80.65   7.815%   $86.9528   $86.95   $86.95   $87.00  
  Purchase #5 $37.28   9.609%   $40.8622   $40.86   $40.85   $40.90  
  Purchase #6 $110.43   5.861%   $116.9023   $116.90   $116.90   $116.90  
  Purchase #7 $175.68   10.352%   $193.8664   $193.87   $193.85   $193.90  
  7 purchase totals = $943.84       $1,034.3568   $1,034.35   $1,034.35   $1,034.40