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 $231.25   5.682%   $244.3896   $244.39   $244.40   $244.40  
  Purchase #2 $75.40   3.122%   $77.754   $77.75   $77.75   $77.80  
  Purchase #3 $54.44   5.628%   $57.5039   $57.50   $57.50   $57.50  
  Purchase #4 $160.34   8.495%   $173.9609   $173.96   $173.95   $174.00  
  Purchase #5 $98.64   11.388%   $109.8731   $109.87   $109.85   $109.90  
  Purchase #6 $91.26   6.844%   $97.5058   $97.51   $97.50   $97.50  
  Purchase #7 $164.52   11.143%   $182.8525   $182.85   $182.85   $182.90  
  7 purchase totals = $875.85       $943.8398   $943.83   $943.80   $944.00