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 $195.72   5.608%   $206.696   $206.70   $206.70   $206.70  
  Purchase #2 $56.25   6.330%   $59.8106   $59.81   $59.80   $59.80  
  Purchase #3 $117.65   12.812%   $132.7233   $132.72   $132.70   $132.70  
  Purchase #4 $11.76   6.655%   $12.5426   $12.54   $12.55   $12.50  
  Purchase #5 $202.42   10.371%   $223.413   $223.41   $223.40   $223.40  
  Purchase #6 $101.78   10.717%   $112.6878   $112.69   $112.70   $112.70  
  Purchase #7 $155.83   13.613%   $177.0431   $177.04   $177.05   $177.00  
  7 purchase totals = $841.41       $924.9164   $924.91   $924.90   $924.80