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 $89.75   4.779%   $94.0392   $94.04   $94.05   $94.00  
  Purchase #2 $19.71   8.471%   $21.3796   $21.38   $21.40   $21.40  
  Purchase #3 $214.33   8.413%   $232.3616   $232.36   $232.35   $232.40  
  Purchase #4 $27.50   9.449%   $30.0985   $30.10   $30.10   $30.10  
  Purchase #5 $232.30   5.164%   $244.296   $244.30   $244.30   $244.30  
  Purchase #6 $118.61   5.261%   $124.8501   $124.85   $124.85   $124.90  
  Purchase #7 $246.54   11.360%   $274.5469   $274.55   $274.55   $274.50  
  7 purchase totals = $948.74       $1,021.5719   $1,021.58   $1,021.60   $1,021.60