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 $204.29   13.540%   $231.9509   $231.95   $231.95   $232.00  
  Purchase #2 $115.81   8.194%   $125.2995   $125.30   $125.30   $125.30  
  Purchase #3 $219.44   3.584%   $227.3047   $227.30   $227.30   $227.30  
  Purchase #4 $80.70   8.159%   $87.2843   $87.28   $87.30   $87.30  
  Purchase #5 $82.89   7.224%   $88.878   $88.88   $88.90   $88.90  
  Purchase #6 $91.35   10.171%   $100.6412   $100.64   $100.65   $100.60  
  Purchase #7 $9.74   8.680%   $10.5854   $10.59   $10.60   $10.60  
  7 purchase totals = $804.22       $871.9440   $871.94   $872.00   $872.00