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 $14.82   8.279%   $16.0469   $16.05   $16.05   $16.00  
  Purchase #2 $250.61   4.276%   $261.3261   $261.33   $261.35   $261.30  
  Purchase #3 $60.94   6.395%   $64.8371   $64.84   $64.85   $64.80  
  Purchase #4 $200.95   11.714%   $224.4893   $224.49   $224.50   $224.50  
  Purchase #5 $145.49   13.512%   $165.1486   $165.15   $165.15   $165.10  
  Purchase #6 $52.93   6.453%   $56.3456   $56.35   $56.35   $56.30  
  Purchase #7 $216.99   11.779%   $242.5493   $242.55   $242.55   $242.50  
  7 purchase totals = $942.73       $1,030.7429   $1,030.76   $1,030.80   $1,030.50