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 $57.42   4.139%   $59.7966   $59.80   $59.80   $59.80  
  Purchase #2 $140.29   3.258%   $144.8606   $144.86   $144.85   $144.90  
  Purchase #3 $186.92   3.611%   $193.6697   $193.67   $193.65   $193.70  
  Purchase #4 $86.49   13.468%   $98.1385   $98.14   $98.15   $98.10  
  Purchase #5 $62.78   6.251%   $66.7044   $66.70   $66.70   $66.70  
  Purchase #6 $248.26   11.541%   $276.9117   $276.91   $276.90   $276.90  
  Purchase #7 $209.43   6.182%   $222.377   $222.38   $222.40   $222.40  
  7 purchase totals = $991.59       $1,062.4585   $1,062.46   $1,062.45   $1,062.50