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 $118.40   6.453%   $126.0404   $126.04   $126.05   $126.00  
  Purchase #2 $56.43   10.328%   $62.2581   $62.26   $62.25   $62.30  
  Purchase #3 $21.26   8.369%   $23.0392   $23.04   $23.05   $23.00  
  Purchase #4 $77.60   5.720%   $82.0387   $82.04   $82.05   $82.00  
  Purchase #5 $190.73   8.180%   $206.3317   $206.33   $206.35   $206.30  
  Purchase #6 $179.89   6.610%   $191.7807   $191.78   $191.80   $191.80  
  Purchase #7 $234.54   6.565%   $249.9376   $249.94   $249.95   $249.90  
  7 purchase totals = $878.85       $941.4264   $941.43   $941.50   $941.30