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 $56.91   7.561%   $61.213   $61.21   $61.20   $61.20  
  Purchase #2 $150.54   11.645%   $168.0704   $168.07   $168.05   $168.10  
  Purchase #3 $237.69   3.779%   $246.6723   $246.67   $246.65   $246.70  
  Purchase #4 $125.29   12.754%   $141.2695   $141.27   $141.25   $141.30  
  Purchase #5 $245.36   8.668%   $266.6278   $266.63   $266.65   $266.60  
  Purchase #6 $42.94   10.554%   $47.4719   $47.47   $47.45   $47.50  
  Purchase #7 $226.45   8.127%   $244.8536   $244.85   $244.85   $244.90  
  7 purchase totals = $1,085.18       $1,176.1785   $1,176.17   $1,176.10   $1,176.30