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 $53.52   13.177%   $60.5723   $60.57   $60.55   $60.60  
  Purchase #2 $21.94   6.662%   $23.4016   $23.40   $23.40   $23.40  
  Purchase #3 $140.26   5.749%   $148.3235   $148.32   $148.30   $148.30  
  Purchase #4 $95.71   6.820%   $102.2374   $102.24   $102.25   $102.20  
  Purchase #5 $214.43   7.507%   $230.5273   $230.53   $230.55   $230.50  
  Purchase #6 $163.50   7.222%   $175.308   $175.31   $175.30   $175.30  
  Purchase #7 $249.58   13.278%   $282.7192   $282.72   $282.70   $282.70  
  7 purchase totals = $938.94       $1,023.0893   $1,023.09   $1,023.05   $1,023.00