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 $241.69   8.782%   $262.9152   $262.92   $262.90   $262.90  
  Purchase #2 $137.63   8.395%   $149.184   $149.18   $149.20   $149.20  
  Purchase #3 $29.46   11.361%   $32.807   $32.81   $32.80   $32.80  
  Purchase #4 $196.72   3.690%   $203.979   $203.98   $204.00   $204.00  
  Purchase #5 $70.85   3.614%   $73.4105   $73.41   $73.40   $73.40  
  Purchase #6 $27.96   11.356%   $31.1351   $31.14   $31.15   $31.10  
  Purchase #7 $18.26   6.629%   $19.4705   $19.47   $19.45   $19.50  
  7 purchase totals = $722.57       $772.9013   $772.91   $772.90   $772.90