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 $112.33   6.193%   $119.2866   $119.29   $119.30   $119.30  
  Purchase #2 $82.82   5.354%   $87.2542   $87.25   $87.25   $87.30  
  Purchase #3 $29.88   11.115%   $33.2012   $33.20   $33.20   $33.20  
  Purchase #4 $223.73   10.393%   $246.9823   $246.98   $247.00   $247.00  
  Purchase #5 $153.61   3.150%   $158.4487   $158.45   $158.45   $158.40  
  Purchase #6 $69.32   4.474%   $72.4214   $72.42   $72.40   $72.40  
  Purchase #7 $201.97   10.467%   $223.1102   $223.11   $223.10   $223.10  
  7 purchase totals = $873.66       $940.7046   $940.70   $940.70   $940.70