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 $50.45   12.726%   $56.8703   $56.87   $56.85   $56.90  
  Purchase #2 $242.31   10.794%   $268.4649   $268.46   $268.45   $268.50  
  Purchase #3 $206.58   6.423%   $219.8486   $219.85   $219.85   $219.80  
  Purchase #4 $65.86   13.441%   $74.7122   $74.71   $74.70   $74.70  
  Purchase #5 $155.64   5.401%   $164.0461   $164.05   $164.05   $164.00  
  Purchase #6 $41.94   10.225%   $46.2284   $46.23   $46.25   $46.20  
  Purchase #7 $86.88   5.748%   $91.8739   $91.87   $91.85   $91.90  
  7 purchase totals = $849.66       $922.0444   $922.04   $922.00   $922.00