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 $203.63   5.189%   $214.1964   $214.20   $214.20   $214.20  
  Purchase #2 $23.85   4.638%   $24.9562   $24.96   $24.95   $25.00  
  Purchase #3 $235.66   6.385%   $250.7069   $250.71   $250.70   $250.70  
  Purchase #4 $83.84   7.525%   $90.149   $90.15   $90.15   $90.10  
  Purchase #5 $97.45   11.106%   $108.2728   $108.27   $108.25   $108.30  
  Purchase #6 $133.99   10.858%   $148.5386   $148.54   $148.55   $148.50  
  Purchase #7 $206.82   12.114%   $231.8742   $231.87   $231.85   $231.90  
  7 purchase totals = $985.24       $1,068.6941   $1,068.70   $1,068.65   $1,068.70