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 $221.77   8.547%   $240.7247   $240.72   $240.70   $240.70  
  Purchase #2 $58.44   6.410%   $62.186   $62.19   $62.20   $62.20  
  Purchase #3 $56.85   6.487%   $60.5379   $60.54   $60.55   $60.50  
  Purchase #4 $191.44   11.746%   $213.9265   $213.93   $213.95   $213.90  
  Purchase #5 $22.85   11.305%   $25.4332   $25.43   $25.45   $25.40  
  Purchase #6 $162.56   8.817%   $176.8929   $176.89   $176.90   $176.90  
  Purchase #7 $234.84   11.522%   $261.8983   $261.90   $261.90   $261.90  
  7 purchase totals = $948.75       $1,041.5995   $1,041.60   $1,041.65   $1,041.50