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 $59.80   8.541%   $64.9075   $64.91   $64.90   $64.90  
  Purchase #2 $183.83   13.262%   $208.2095   $208.21   $208.20   $208.20  
  Purchase #3 $24.30   12.868%   $27.4269   $27.43   $27.45   $27.40  
  Purchase #4 $245.30   4.829%   $257.1455   $257.15   $257.15   $257.10  
  Purchase #5 $41.87   10.560%   $46.2915   $46.29   $46.30   $46.30  
  Purchase #6 $154.58   12.155%   $173.3692   $173.37   $173.35   $173.40  
  Purchase #7 $235.48   3.832%   $244.5036   $244.50   $244.50   $244.50  
  7 purchase totals = $945.16       $1,021.8537   $1,021.86   $1,021.85   $1,021.80