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 $61.79   6.211%   $65.6278   $65.63   $65.65   $65.60  
  Purchase #2 $204.99   4.337%   $213.8804   $213.88   $213.90   $213.90  
  Purchase #3 $60.32   9.381%   $65.9786   $65.98   $66.00   $66.00  
  Purchase #4 $233.35   9.517%   $255.5579   $255.56   $255.55   $255.60  
  Purchase #5 $248.76   9.718%   $272.9345   $272.93   $272.95   $272.90  
  Purchase #6 $34.66   11.108%   $38.51   $38.51   $38.50   $38.50  
  Purchase #7 $39.34   7.252%   $42.1929   $42.19   $42.20   $42.20  
  7 purchase totals = $883.21       $954.6821   $954.68   $954.75   $954.70