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 $203.35   13.714%   $231.2374   $231.24   $231.25   $231.20  
  Purchase #2 $208.48   10.635%   $230.6518   $230.65   $230.65   $230.70  
  Purchase #3 $120.28   4.633%   $125.8526   $125.85   $125.85   $125.90  
  Purchase #4 $201.43   3.237%   $207.9503   $207.95   $207.95   $208.00  
  Purchase #5 $126.61   4.142%   $131.8542   $131.85   $131.85   $131.90  
  Purchase #6 $229.86   5.814%   $243.2241   $243.22   $243.20   $243.20  
  Purchase #7 $153.70   4.845%   $161.1468   $161.15   $161.15   $161.10  
  7 purchase totals = $1,243.71       $1,331.9172   $1,331.91   $1,331.90   $1,332.00