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 $222.64   9.122%   $242.9492   $242.95   $242.95   $242.90  
  Purchase #2 $24.39   6.699%   $26.0239   $26.02   $26.00   $26.00  
  Purchase #3 $50.33   8.850%   $54.7842   $54.78   $54.80   $54.80  
  Purchase #4 $248.86   10.664%   $275.3984   $275.40   $275.40   $275.40  
  Purchase #5 $179.33   4.406%   $187.2313   $187.23   $187.25   $187.20  
  Purchase #6 $35.90   7.303%   $38.5218   $38.52   $38.50   $38.50  
  Purchase #7 $125.86   5.185%   $132.3858   $132.39   $132.40   $132.40  
  7 purchase totals = $887.31       $957.2946   $957.29   $957.30   $957.20