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 $217.75   13.708%   $247.5992   $247.60   $247.60   $247.60  
  Purchase #2 $237.37   9.646%   $260.2667   $260.27   $260.25   $260.30  
  Purchase #3 $194.44   7.492%   $209.0074   $209.01   $209.00   $209.00  
  Purchase #4 $81.49   10.386%   $89.9536   $89.95   $89.95   $90.00  
  Purchase #5 $156.65   6.686%   $167.1236   $167.12   $167.10   $167.10  
  Purchase #6 $152.53   10.126%   $167.9752   $167.98   $168.00   $168.00  
  Purchase #7 $31.46   12.268%   $35.3195   $35.32   $35.30   $35.30  
  7 purchase totals = $1,071.69       $1,177.2452   $1,177.25   $1,177.20   $1,177.30