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 $215.77   13.373%   $244.6249   $244.62   $244.60   $244.60  
  Purchase #2 $110.52   4.572%   $115.573   $115.57   $115.55   $115.60  
  Purchase #3 $22.36   11.705%   $24.9772   $24.98   $25.00   $25.00  
  Purchase #4 $127.31   7.269%   $136.5642   $136.56   $136.55   $136.60  
  Purchase #5 $114.49   13.767%   $130.2518   $130.25   $130.25   $130.30  
  Purchase #6 $248.97   4.281%   $259.6284   $259.63   $259.65   $259.60  
  Purchase #7 $210.53   10.724%   $233.1072   $233.11   $233.10   $233.10  
  7 purchase totals = $1,049.95       $1,144.7267   $1,144.72   $1,144.70   $1,144.80