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 $227.72   8.437%   $246.9327   $246.93   $246.95   $246.90  
  Purchase #2 $151.29   4.275%   $157.7576   $157.76   $157.75   $157.80  
  Purchase #3 $173.90   4.203%   $181.209   $181.21   $181.20   $181.20  
  Purchase #4 $61.28   5.408%   $64.594   $64.59   $64.60   $64.60  
  Purchase #5 $89.52   12.233%   $100.471   $100.47   $100.45   $100.50  
  Purchase #6 $174.95   4.752%   $183.2636   $183.26   $183.25   $183.30  
  Purchase #7 $199.75   13.401%   $226.5185   $226.52   $226.50   $226.50  
  7 purchase totals = $1,078.41       $1,160.7464   $1,160.74   $1,160.70   $1,160.80