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 $208.47   12.177%   $233.8554   $233.86   $233.85   $233.90  
  Purchase #2 $16.74   4.575%   $17.5059   $17.51   $17.50   $17.50  
  Purchase #3 $249.32   12.290%   $279.9614   $279.96   $279.95   $280.00  
  Purchase #4 $50.76   12.363%   $57.0355   $57.04   $57.05   $57.00  
  Purchase #5 $138.79   12.437%   $156.0513   $156.05   $156.05   $156.10  
  Purchase #6 $194.49   3.212%   $200.737   $200.74   $200.75   $200.70  
  Purchase #7 $69.34   8.243%   $75.0557   $75.06   $75.05   $75.10  
  7 purchase totals = $927.91       $1,020.2022   $1,020.22   $1,020.20   $1,020.30