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 $50.48   10.235%   $55.6466   $55.65   $55.65   $55.60  
  Purchase #2 $95.30   11.442%   $106.2042   $106.20   $106.20   $106.20  
  Purchase #3 $112.27   5.525%   $118.4729   $118.47   $118.45   $118.50  
  Purchase #4 $70.73   4.551%   $73.9489   $73.95   $73.95   $73.90  
  Purchase #5 $231.66   9.213%   $253.0028   $253.00   $253.00   $253.00  
  Purchase #6 $187.40   5.110%   $196.9761   $196.98   $197.00   $197.00  
  Purchase #7 $74.59   3.785%   $77.4132   $77.41   $77.40   $77.40  
  7 purchase totals = $822.43       $881.6647   $881.66   $881.65   $881.60