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 $219.44   6.177%   $232.9948   $232.99   $233.00   $233.00  
  Purchase #2 $247.71   9.115%   $270.2888   $270.29   $270.30   $270.30  
  Purchase #3 $124.99   9.319%   $136.6378   $136.64   $136.65   $136.60  
  Purchase #4 $232.41   12.173%   $260.7013   $260.70   $260.70   $260.70  
  Purchase #5 $117.90   4.741%   $123.4896   $123.49   $123.50   $123.50  
  Purchase #6 $44.42   8.274%   $48.0953   $48.10   $48.10   $48.10  
  Purchase #7 $163.25   3.762%   $169.3915   $169.39   $169.40   $169.40  
  7 purchase totals = $1,150.12       $1,241.5991   $1,241.60   $1,241.65   $1,241.60