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 $246.26   9.559%   $269.8   $269.80   $269.80   $269.80  
  Purchase #2 $179.71   5.240%   $189.1268   $189.13   $189.15   $189.10  
  Purchase #3 $48.89   3.502%   $50.6021   $50.60   $50.60   $50.60  
  Purchase #4 $39.33   5.244%   $41.3925   $41.39   $41.40   $41.40  
  Purchase #5 $5.92   12.389%   $6.6534   $6.65   $6.65   $6.70  
  Purchase #6 $89.26   10.559%   $98.685   $98.69   $98.70   $98.70  
  Purchase #7 $243.54   10.153%   $268.2666   $268.27   $268.25   $268.30  
  7 purchase totals = $852.91       $924.5264   $924.53   $924.55   $924.60