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 $84.30   11.485%   $93.9819   $93.98   $94.00   $94.00  
  Purchase #2 $157.93   12.622%   $177.8639   $177.86   $177.85   $177.90  
  Purchase #3 $85.95   8.493%   $93.2497   $93.25   $93.25   $93.20  
  Purchase #4 $243.91   7.867%   $263.0984   $263.10   $263.10   $263.10  
  Purchase #5 $144.76   5.687%   $152.9925   $152.99   $153.00   $153.00  
  Purchase #6 $14.89   10.592%   $16.4671   $16.47   $16.45   $16.50  
  Purchase #7 $126.92   5.785%   $134.2623   $134.26   $134.25   $134.30  
  7 purchase totals = $858.66       $931.9158   $931.91   $931.90   $932.00