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 $54.33   10.673%   $60.1286   $60.13   $60.15   $60.10  
  Purchase #2 $177.31   4.689%   $185.6241   $185.62   $185.60   $185.60  
  Purchase #3 $11.94   9.821%   $13.1126   $13.11   $13.10   $13.10  
  Purchase #4 $197.86   8.390%   $214.4605   $214.46   $214.45   $214.50  
  Purchase #5 $43.29   10.653%   $47.9017   $47.90   $47.90   $47.90  
  Purchase #6 $215.79   7.695%   $232.395   $232.40   $232.40   $232.40  
  Purchase #7 $250.25   6.143%   $265.6229   $265.62   $265.60   $265.60  
  7 purchase totals = $950.77       $1,019.2454   $1,019.24   $1,019.20   $1,019.20