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 $232.94   9.597%   $255.2953   $255.30   $255.30   $255.30  
  Purchase #2 $213.54   8.692%   $232.1009   $232.10   $232.10   $232.10  
  Purchase #3 $78.61   11.504%   $87.6533   $87.65   $87.65   $87.70  
  Purchase #4 $145.33   13.193%   $164.5034   $164.50   $164.50   $164.50  
  Purchase #5 $8.65   3.873%   $8.985   $8.99   $9.00   $9.00  
  Purchase #6 $145.95   7.445%   $156.816   $156.82   $156.80   $156.80  
  Purchase #7 $33.85   6.853%   $36.1697   $36.17   $36.15   $36.20  
  7 purchase totals = $858.87       $941.5236   $941.53   $941.50   $941.60