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 $54.97   10.661%   $60.8304   $60.83   $60.85   $60.80  
  Purchase #2 $63.41   9.799%   $69.6235   $69.62   $69.60   $69.60  
  Purchase #3 $84.90   9.136%   $92.6565   $92.66   $92.65   $92.70  
  Purchase #4 $24.56   11.284%   $27.3314   $27.33   $27.35   $27.30  
  Purchase #5 $138.33   13.505%   $157.0115   $157.01   $157.00   $157.00  
  Purchase #6 $188.54   5.743%   $199.3679   $199.37   $199.35   $199.40  
  Purchase #7 $139.30   4.769%   $145.9432   $145.94   $145.95   $145.90  
  7 purchase totals = $694.01       $752.7644   $752.76   $752.75   $752.70