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 $84.92   3.709%   $88.0697   $88.07   $88.05   $88.10  
  Purchase #2 $119.54   9.535%   $130.9381   $130.94   $130.95   $130.90  
  Purchase #3 $43.99   5.755%   $46.5216   $46.52   $46.50   $46.50  
  Purchase #4 $23.58   13.348%   $26.7275   $26.73   $26.75   $26.70  
  Purchase #5 $234.27   6.275%   $248.9704   $248.97   $248.95   $249.00  
  Purchase #6 $191.58   9.197%   $209.1996   $209.20   $209.20   $209.20  
  Purchase #7 $192.52   6.275%   $204.6006   $204.60   $204.60   $204.60  
  7 purchase totals = $890.40       $955.0275   $955.03   $955.00   $955.00