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 $200.75   8.391%   $217.5949   $217.59   $217.60   $217.60  
  Purchase #2 $150.33   11.102%   $167.0196   $167.02   $167.00   $167.00  
  Purchase #3 $227.58   4.447%   $237.7005   $237.70   $237.70   $237.70  
  Purchase #4 $17.60   9.646%   $19.2977   $19.30   $19.30   $19.30  
  Purchase #5 $170.29   9.452%   $186.3858   $186.39   $186.40   $186.40  
  Purchase #6 $241.58   7.734%   $260.2638   $260.26   $260.25   $260.30  
  Purchase #7 $54.71   9.696%   $60.0147   $60.01   $60.00   $60.00  
  7 purchase totals = $1,062.84       $1,148.2770   $1,148.27   $1,148.25   $1,148.30