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 $58.62   11.860%   $65.5723   $65.57   $65.55   $65.60  
  Purchase #2 $62.46   4.483%   $65.2601   $65.26   $65.25   $65.30  
  Purchase #3 $213.94   9.501%   $234.2664   $234.27   $234.25   $234.30  
  Purchase #4 $66.42   4.675%   $69.5251   $69.53   $69.55   $69.50  
  Purchase #5 $154.75   10.458%   $170.9338   $170.93   $170.95   $170.90  
  Purchase #6 $204.70   7.244%   $219.5285   $219.53   $219.55   $219.50  
  Purchase #7 $146.40   9.860%   $160.835   $160.84   $160.85   $160.80  
  7 purchase totals = $907.29       $985.9212   $985.93   $985.95   $985.90