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 $190.29   7.523%   $204.6055   $204.61   $204.60   $204.60  
  Purchase #2 $148.68   8.582%   $161.4397   $161.44   $161.45   $161.40  
  Purchase #3 $25.33   13.303%   $28.6996   $28.70   $28.70   $28.70  
  Purchase #4 $61.80   8.353%   $66.9622   $66.96   $66.95   $67.00  
  Purchase #5 $144.49   7.261%   $154.9814   $154.98   $155.00   $155.00  
  Purchase #6 $245.48   10.507%   $271.2726   $271.27   $271.25   $271.30  
  Purchase #7 $234.87   10.234%   $258.9066   $258.91   $258.90   $258.90  
  7 purchase totals = $1,050.94       $1,146.8676   $1,146.87   $1,146.85   $1,146.90