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 $23.83   6.407%   $25.3568   $25.36   $25.35   $25.40  
  Purchase #2 $195.37   4.357%   $203.8823   $203.88   $203.90   $203.90  
  Purchase #3 $168.53   5.603%   $177.9727   $177.97   $177.95   $178.00  
  Purchase #4 $163.87   13.603%   $186.1612   $186.16   $186.15   $186.20  
  Purchase #5 $7.75   5.126%   $8.1473   $8.15   $8.15   $8.10  
  Purchase #6 $221.26   10.712%   $244.9614   $244.96   $244.95   $245.00  
  Purchase #7 $100.82   7.324%   $108.2041   $108.20   $108.20   $108.20  
  7 purchase totals = $881.43       $954.6858   $954.68   $954.65   $954.80