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 $46.41   7.761%   $50.0119   $50.01   $50.00   $50.00  
  Purchase #2 $191.74   3.397%   $198.2534   $198.25   $198.25   $198.30  
  Purchase #3 $55.40   6.269%   $58.873   $58.87   $58.85   $58.90  
  Purchase #4 $27.75   12.412%   $31.1943   $31.19   $31.20   $31.20  
  Purchase #5 $72.87   7.220%   $78.1312   $78.13   $78.15   $78.10  
  Purchase #6 $180.97   4.782%   $189.624   $189.62   $189.60   $189.60  
  Purchase #7 $101.48   11.354%   $113.002   $113.00   $113.00   $113.00  
  7 purchase totals = $676.62       $719.0898   $719.07   $719.05   $719.10