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 $204.43   9.798%   $224.4601   $224.46   $224.45   $224.50  
  Purchase #2 $219.55   13.480%   $249.1453   $249.15   $249.15   $249.10  
  Purchase #3 $115.79   5.864%   $122.5799   $122.58   $122.60   $122.60  
  Purchase #4 $152.43   5.784%   $161.2466   $161.25   $161.25   $161.20  
  Purchase #5 $32.48   10.844%   $36.0021   $36.00   $36.00   $36.00  
  Purchase #6 $218.53   7.722%   $235.4049   $235.40   $235.40   $235.40  
  Purchase #7 $204.26   6.705%   $217.9556   $217.96   $217.95   $218.00  
  7 purchase totals = $1,147.47       $1,246.7945   $1,246.80   $1,246.80   $1,246.80