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 $235.26   4.256%   $245.2727   $245.27   $245.25   $245.30  
  Purchase #2 $177.71   4.126%   $185.0423   $185.04   $185.05   $185.00  
  Purchase #3 $154.34   6.788%   $164.8166   $164.82   $164.80   $164.80  
  Purchase #4 $183.48   5.561%   $193.6833   $193.68   $193.70   $193.70  
  Purchase #5 $215.33   6.332%   $228.9647   $228.96   $228.95   $229.00  
  Purchase #6 $113.63   7.583%   $122.2466   $122.25   $122.25   $122.20  
  Purchase #7 $223.81   4.838%   $234.6379   $234.64   $234.65   $234.60  
  7 purchase totals = $1,303.56       $1,374.6641   $1,374.66   $1,374.65   $1,374.60