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 $89.80   6.331%   $95.4852   $95.49   $95.50   $95.50  
  Purchase #2 $174.40   11.857%   $195.0786   $195.08   $195.10   $195.10  
  Purchase #3 $65.62   9.663%   $71.9609   $71.96   $71.95   $72.00  
  Purchase #4 $244.98   6.865%   $261.7979   $261.80   $261.80   $261.80  
  Purchase #5 $14.75   3.731%   $15.3003   $15.30   $15.30   $15.30  
  Purchase #6 $199.90   11.294%   $222.4767   $222.48   $222.50   $222.50  
  Purchase #7 $59.58   3.625%   $61.7398   $61.74   $61.75   $61.70  
  7 purchase totals = $849.03       $923.8394   $923.85   $923.90   $923.90