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 $29.34   11.183%   $32.6211   $32.62   $32.60   $32.60  
  Purchase #2 $153.73   11.236%   $171.0031   $171.00   $171.00   $171.00  
  Purchase #3 $204.99   3.677%   $212.5275   $212.53   $212.55   $212.50  
  Purchase #4 $167.76   5.811%   $177.5085   $177.51   $177.50   $177.50  
  Purchase #5 $119.85   8.665%   $130.235   $130.24   $130.25   $130.20  
  Purchase #6 $234.73   9.619%   $257.3087   $257.31   $257.30   $257.30  
  Purchase #7 $179.65   9.237%   $196.2443   $196.24   $196.25   $196.20  
  7 purchase totals = $1,090.05       $1,177.4482   $1,177.45   $1,177.45   $1,177.30