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 $59.95   8.573%   $65.0895   $65.09   $65.10   $65.10  
  Purchase #2 $52.28   10.694%   $57.8708   $57.87   $57.85   $57.90  
  Purchase #3 $249.82   13.152%   $282.6763   $282.68   $282.70   $282.70  
  Purchase #4 $31.27   11.369%   $34.8251   $34.83   $34.85   $34.80  
  Purchase #5 $174.72   5.342%   $184.0535   $184.05   $184.05   $184.10  
  Purchase #6 $94.26   9.164%   $102.898   $102.90   $102.90   $102.90  
  Purchase #7 $215.82   11.359%   $240.335   $240.34   $240.35   $240.30  
  7 purchase totals = $878.12       $967.7482   $967.76   $967.80   $967.80