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 $216.58   9.855%   $237.924   $237.92   $237.90   $237.90  
  Purchase #2 $85.33   12.666%   $96.1379   $96.14   $96.15   $96.10  
  Purchase #3 $109.45   7.576%   $117.7419   $117.74   $117.75   $117.70  
  Purchase #4 $200.66   5.757%   $212.212   $212.21   $212.20   $212.20  
  Purchase #5 $153.61   12.766%   $173.2199   $173.22   $173.20   $173.20  
  Purchase #6 $16.35   11.732%   $18.2682   $18.27   $18.25   $18.30  
  Purchase #7 $160.48   4.807%   $168.1943   $168.19   $168.20   $168.20  
  7 purchase totals = $942.46       $1,023.6982   $1,023.69   $1,023.65   $1,023.60