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 $74.91   13.768%   $85.2236   $85.22   $85.20   $85.20  
  Purchase #2 $76.72   8.607%   $83.3233   $83.32   $83.30   $83.30  
  Purchase #3 $213.29   6.700%   $227.5804   $227.58   $227.60   $227.60  
  Purchase #4 $155.43   8.723%   $168.9882   $168.99   $169.00   $169.00  
  Purchase #5 $250.82   5.624%   $264.9261   $264.93   $264.95   $264.90  
  Purchase #6 $121.53   9.662%   $133.2722   $133.27   $133.25   $133.30  
  Purchase #7 $91.57   6.587%   $97.6017   $97.60   $97.60   $97.60  
  7 purchase totals = $984.27       $1,060.9155   $1,060.91   $1,060.90   $1,060.90