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 $32.49   5.440%   $34.2575   $34.26   $34.25   $34.30  
  Purchase #2 $215.50   10.418%   $237.9508   $237.95   $237.95   $238.00  
  Purchase #3 $246.62   8.251%   $266.9686   $266.97   $266.95   $267.00  
  Purchase #4 $42.98   12.699%   $48.438   $48.44   $48.45   $48.40  
  Purchase #5 $67.58   6.601%   $72.041   $72.04   $72.05   $72.00  
  Purchase #6 $192.67   6.391%   $204.9835   $204.98   $205.00   $205.00  
  Purchase #7 $56.63   12.709%   $63.8271   $63.83   $63.85   $63.80  
  7 purchase totals = $854.47       $928.4665   $928.47   $928.50   $928.50