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 $125.94   4.605%   $131.7395   $131.74   $131.75   $131.70  
  Purchase #2 $41.39   7.266%   $44.3974   $44.40   $44.40   $44.40  
  Purchase #3 $123.65   11.516%   $137.8895   $137.89   $137.90   $137.90  
  Purchase #4 $57.27   6.153%   $60.7938   $60.79   $60.80   $60.80  
  Purchase #5 $88.81   10.308%   $97.9645   $97.96   $97.95   $98.00  
  Purchase #6 $202.79   5.865%   $214.6836   $214.68   $214.70   $214.70  
  Purchase #7 $220.60   11.633%   $246.2624   $246.26   $246.25   $246.30  
  7 purchase totals = $860.45       $933.7307   $933.72   $933.75   $933.80