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 $112.58   6.120%   $119.4699   $119.47   $119.45   $119.50  
  Purchase #2 $127.75   6.374%   $135.8928   $135.89   $135.90   $135.90  
  Purchase #3 $62.44   11.657%   $69.7186   $69.72   $69.70   $69.70  
  Purchase #4 $250.49   4.251%   $261.1383   $261.14   $261.15   $261.10  
  Purchase #5 $206.63   9.348%   $225.9458   $225.95   $225.95   $225.90  
  Purchase #6 $167.58   7.286%   $179.7899   $179.79   $179.80   $179.80  
  Purchase #7 $156.93   5.725%   $165.9142   $165.91   $165.90   $165.90  
  7 purchase totals = $1,084.40       $1,157.8695   $1,157.87   $1,157.85   $1,157.80