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 $236.61   4.605%   $247.5059   $247.51   $247.50   $247.50  
  Purchase #2 $134.46   11.729%   $150.2308   $150.23   $150.25   $150.20  
  Purchase #3 $244.52   4.866%   $256.4183   $256.42   $256.40   $256.40  
  Purchase #4 $173.69   5.827%   $183.8109   $183.81   $183.80   $183.80  
  Purchase #5 $248.68   8.835%   $270.6509   $270.65   $270.65   $270.70  
  Purchase #6 $196.69   4.624%   $205.7849   $205.78   $205.80   $205.80  
  Purchase #7 $127.37   6.620%   $135.8019   $135.80   $135.80   $135.80  
  7 purchase totals = $1,362.02       $1,450.2036   $1,450.20   $1,450.20   $1,450.20