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 $91.49   4.449%   $95.5604   $95.56   $95.55   $95.60  
  Purchase #2 $60.96   4.440%   $63.6666   $63.67   $63.65   $63.70  
  Purchase #3 $126.79   7.736%   $136.5985   $136.60   $136.60   $136.60  
  Purchase #4 $229.34   12.802%   $258.7001   $258.70   $258.70   $258.70  
  Purchase #5 $221.81   13.401%   $251.5348   $251.53   $251.55   $251.50  
  Purchase #6 $34.93   5.109%   $36.7146   $36.71   $36.70   $36.70  
  Purchase #7 $108.61   11.572%   $121.1783   $121.18   $121.20   $121.20  
  7 purchase totals = $873.93       $963.9533   $963.95   $963.95   $964.00