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 $249.78   10.581%   $276.2092   $276.21   $276.20   $276.20  
  Purchase #2 $119.86   11.131%   $133.2016   $133.20   $133.20   $133.20  
  Purchase #3 $249.71   8.765%   $271.5971   $271.60   $271.60   $271.60  
  Purchase #4 $126.43   12.697%   $142.4828   $142.48   $142.50   $142.50  
  Purchase #5 $62.95   8.441%   $68.2636   $68.26   $68.25   $68.30  
  Purchase #6 $232.57   13.804%   $264.674   $264.67   $264.65   $264.70  
  Purchase #7 $22.26   10.825%   $24.6696   $24.67   $24.65   $24.70  
  7 purchase totals = $1,063.56       $1,181.0979   $1,181.09   $1,181.05   $1,181.20