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 $226.27   11.793%   $252.954   $252.95   $252.95   $253.00  
  Purchase #2 $92.59   9.659%   $101.5333   $101.53   $101.55   $101.50  
  Purchase #3 $160.78   8.567%   $174.554   $174.55   $174.55   $174.60  
  Purchase #4 $104.32   10.166%   $114.9252   $114.93   $114.95   $114.90  
  Purchase #5 $66.76   10.817%   $73.9814   $73.98   $74.00   $74.00  
  Purchase #6 $90.58   8.517%   $98.2947   $98.29   $98.30   $98.30  
  Purchase #7 $110.26   12.327%   $123.8518   $123.85   $123.85   $123.90  
  7 purchase totals = $851.56       $940.0944   $940.08   $940.15   $940.20