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 $156.65   10.604%   $173.2612   $173.26   $173.25   $173.30  
  Purchase #2 $217.60   10.260%   $239.9258   $239.93   $239.95   $239.90  
  Purchase #3 $228.98   7.853%   $246.9618   $246.96   $246.95   $247.00  
  Purchase #4 $17.65   8.516%   $19.1531   $19.15   $19.15   $19.20  
  Purchase #5 $228.94   6.417%   $243.6311   $243.63   $243.65   $243.60  
  Purchase #6 $233.75   5.222%   $245.9564   $245.96   $245.95   $246.00  
  Purchase #7 $118.69   11.430%   $132.2563   $132.26   $132.25   $132.30  
  7 purchase totals = $1,202.26       $1,301.1457   $1,301.15   $1,301.15   $1,301.30