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 $52.84   13.487%   $59.9665   $59.97   $59.95   $60.00  
  Purchase #2 $8.60   8.573%   $9.3373   $9.34   $9.35   $9.30  
  Purchase #3 $244.53   13.376%   $277.2383   $277.24   $277.25   $277.20  
  Purchase #4 $208.39   3.819%   $216.3484   $216.35   $216.35   $216.30  
  Purchase #5 $229.80   9.384%   $251.3644   $251.36   $251.35   $251.40  
  Purchase #6 $95.27   12.827%   $107.4903   $107.49   $107.50   $107.50  
  Purchase #7 $63.39   3.772%   $65.7811   $65.78   $65.80   $65.80  
  7 purchase totals = $902.82       $987.5263   $987.53   $987.55   $987.50