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 $199.44   8.180%   $215.7542   $215.75   $215.75   $215.80  
  Purchase #2 $62.45   3.850%   $64.8543   $64.85   $64.85   $64.90  
  Purchase #3 $197.68   12.169%   $221.7357   $221.74   $221.75   $221.70  
  Purchase #4 $141.27   6.118%   $149.9129   $149.91   $149.90   $149.90  
  Purchase #5 $191.37   6.252%   $203.3345   $203.33   $203.35   $203.30  
  Purchase #6 $152.46   3.245%   $157.4073   $157.41   $157.40   $157.40  
  Purchase #7 $226.50   13.175%   $256.3414   $256.34   $256.35   $256.30  
  7 purchase totals = $1,171.17       $1,269.3403   $1,269.33   $1,269.35   $1,269.30