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 $75.36   12.505%   $84.7838   $84.78   $84.80   $84.80  
  Purchase #2 $53.61   11.746%   $59.907   $59.91   $59.90   $59.90  
  Purchase #3 $21.61   7.536%   $23.2385   $23.24   $23.25   $23.20  
  Purchase #4 $225.57   6.672%   $240.62   $240.62   $240.60   $240.60  
  Purchase #5 $163.86   9.674%   $179.7118   $179.71   $179.70   $179.70  
  Purchase #6 $142.71   8.512%   $154.8575   $154.86   $154.85   $154.90  
  Purchase #7 $184.72   12.564%   $207.9282   $207.93   $207.95   $207.90  
  7 purchase totals = $867.44       $951.0468   $951.05   $951.05   $951.00