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 $99.75   9.342%   $109.0686   $109.07   $109.05   $109.10  
  Purchase #2 $216.64   12.817%   $244.4067   $244.41   $244.40   $244.40  
  Purchase #3 $75.86   12.644%   $85.4517   $85.45   $85.45   $85.50  
  Purchase #4 $25.56   8.129%   $27.6378   $27.64   $27.65   $27.60  
  Purchase #5 $120.34   12.212%   $135.0359   $135.04   $135.05   $135.00  
  Purchase #6 $130.81   7.718%   $140.9059   $140.91   $140.90   $140.90  
  Purchase #7 $82.53   5.199%   $86.8207   $86.82   $86.80   $86.80  
  7 purchase totals = $751.49       $829.3273   $829.34   $829.30   $829.30