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 $24.82   9.591%   $27.2005   $27.20   $27.20   $27.20  
  Purchase #2 $246.96   3.407%   $255.3739   $255.37   $255.35   $255.40  
  Purchase #3 $163.98   4.119%   $170.7343   $170.73   $170.75   $170.70  
  Purchase #4 $232.88   13.386%   $264.0533   $264.05   $264.05   $264.10  
  Purchase #5 $105.62   9.298%   $115.4405   $115.44   $115.45   $115.40  
  Purchase #6 $29.58   9.171%   $32.2928   $32.29   $32.30   $32.30  
  Purchase #7 $24.87   9.283%   $27.1787   $27.18   $27.20   $27.20  
  7 purchase totals = $828.71       $892.2740   $892.26   $892.30   $892.30