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 $67.48   8.207%   $73.0181   $73.02   $73.00   $73.00  
  Purchase #2 $92.44   5.809%   $97.8098   $97.81   $97.80   $97.80  
  Purchase #3 $156.64   12.105%   $175.6013   $175.60   $175.60   $175.60  
  Purchase #4 $240.81   9.274%   $263.1427   $263.14   $263.15   $263.10  
  Purchase #5 $88.97   3.823%   $92.3713   $92.37   $92.35   $92.40  
  Purchase #6 $53.53   3.443%   $55.373   $55.37   $55.35   $55.40  
  Purchase #7 $43.65   6.853%   $46.6413   $46.64   $46.65   $46.60  
  7 purchase totals = $743.52       $803.9575   $803.95   $803.90   $803.90