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 $55.77   12.401%   $62.686   $62.69   $62.70   $62.70  
  Purchase #2 $60.44   12.109%   $67.7587   $67.76   $67.75   $67.80  
  Purchase #3 $91.34   6.128%   $96.9373   $96.94   $96.95   $96.90  
  Purchase #4 $152.90   5.216%   $160.8753   $160.88   $160.90   $160.90  
  Purchase #5 $135.79   13.570%   $154.2167   $154.22   $154.20   $154.20  
  Purchase #6 $180.45   3.348%   $186.4915   $186.49   $186.50   $186.50  
  Purchase #7 $133.89   4.857%   $140.393   $140.39   $140.40   $140.40  
  7 purchase totals = $810.58       $869.3585   $869.37   $869.40   $869.40