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 $178.93   8.774%   $194.6293   $194.63   $194.65   $194.60  
  Purchase #2 $218.51   4.210%   $227.7093   $227.71   $227.70   $227.70  
  Purchase #3 $215.71   12.247%   $242.128   $242.13   $242.15   $242.10  
  Purchase #4 $79.26   4.334%   $82.6951   $82.70   $82.70   $82.70  
  Purchase #5 $198.68   7.492%   $213.5651   $213.57   $213.55   $213.60  
  Purchase #6 $6.62   13.244%   $7.4968   $7.50   $7.50   $7.50  
  Purchase #7 $60.88   12.865%   $68.7122   $68.71   $68.70   $68.70  
  7 purchase totals = $958.59       $1,036.9358   $1,036.95   $1,036.95   $1,036.90