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 $244.67   9.335%   $267.5099   $267.51   $267.50   $267.50  
  Purchase #2 $121.31   11.296%   $135.0132   $135.01   $135.00   $135.00  
  Purchase #3 $46.34   3.859%   $48.1283   $48.13   $48.15   $48.10  
  Purchase #4 $188.93   4.306%   $197.0653   $197.07   $197.05   $197.10  
  Purchase #5 $163.53   7.561%   $175.8945   $175.89   $175.90   $175.90  
  Purchase #6 $78.25   7.152%   $83.8464   $83.85   $83.85   $83.80  
  Purchase #7 $215.32   5.319%   $226.7729   $226.77   $226.75   $226.80  
  7 purchase totals = $1,058.35       $1,134.2305   $1,134.23   $1,134.20   $1,134.20