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 $237.50   9.623%   $260.3546   $260.35   $260.35   $260.40  
  Purchase #2 $229.55   7.298%   $246.3026   $246.30   $246.30   $246.30  
  Purchase #3 $62.65   3.554%   $64.8766   $64.88   $64.90   $64.90  
  Purchase #4 $167.47   3.392%   $173.1506   $173.15   $173.15   $173.20  
  Purchase #5 $186.35   9.861%   $204.726   $204.73   $204.75   $204.70  
  Purchase #6 $159.92   9.432%   $175.0037   $175.00   $175.00   $175.00  
  Purchase #7 $162.73   4.740%   $170.4434   $170.44   $170.45   $170.40  
  7 purchase totals = $1,206.17       $1,294.8575   $1,294.85   $1,294.90   $1,294.90