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 $176.81   13.288%   $200.3045   $200.30   $200.30   $200.30  
  Purchase #2 $12.74   4.272%   $13.2843   $13.28   $13.30   $13.30  
  Purchase #3 $227.58   7.522%   $244.6986   $244.70   $244.70   $244.70  
  Purchase #4 $174.53   9.443%   $191.0109   $191.01   $191.00   $191.00  
  Purchase #5 $123.55   8.417%   $133.9492   $133.95   $133.95   $133.90  
  Purchase #6 $182.73   5.633%   $193.0232   $193.02   $193.00   $193.00  
  Purchase #7 $45.61   4.729%   $47.7669   $47.77   $47.75   $47.80  
  7 purchase totals = $943.55       $1,024.0376   $1,024.03   $1,024.00   $1,024.00