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 $87.73   11.143%   $97.5058   $97.51   $97.50   $97.50  
  Purchase #2 $82.42   11.237%   $91.6815   $91.68   $91.70   $91.70  
  Purchase #3 $221.74   12.432%   $249.3067   $249.31   $249.30   $249.30  
  Purchase #4 $233.95   11.555%   $260.9829   $260.98   $261.00   $261.00  
  Purchase #5 $196.44   5.107%   $206.4722   $206.47   $206.45   $206.50  
  Purchase #6 $34.63   13.330%   $39.2462   $39.25   $39.25   $39.20  
  Purchase #7 $118.58   11.124%   $131.7708   $131.77   $131.75   $131.80  
  7 purchase totals = $975.49       $1,076.9661   $1,076.97   $1,076.95   $1,077.00