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 $60.44   12.292%   $67.8693   $67.87   $67.85   $67.90  
  Purchase #2 $119.51   11.667%   $133.4532   $133.45   $133.45   $133.50  
  Purchase #3 $122.36   5.670%   $129.2978   $129.30   $129.30   $129.30  
  Purchase #4 $82.54   11.340%   $91.9   $91.90   $91.90   $91.90  
  Purchase #5 $18.46   5.771%   $19.5253   $19.53   $19.55   $19.50  
  Purchase #6 $129.97   11.743%   $145.2324   $145.23   $145.25   $145.20  
  Purchase #7 $177.35   4.572%   $185.4584   $185.46   $185.45   $185.50  
  7 purchase totals = $710.63       $772.7364   $772.74   $772.75   $772.80