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 $10.73   13.615%   $12.1909   $12.19   $12.20   $12.20  
  Purchase #2 $163.29   6.621%   $174.1014   $174.10   $174.10   $174.10  
  Purchase #3 $49.95   6.253%   $53.0734   $53.07   $53.05   $53.10  
  Purchase #4 $250.92   4.547%   $262.3293   $262.33   $262.35   $262.30  
  Purchase #5 $143.83   10.427%   $158.8272   $158.83   $158.85   $158.80  
  Purchase #6 $66.28   3.385%   $68.5236   $68.52   $68.50   $68.50  
  Purchase #7 $197.71   11.760%   $220.9607   $220.96   $220.95   $221.00  
  7 purchase totals = $882.71       $950.0065   $950.00   $950.00   $950.00