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 $158.82   5.548%   $167.6313   $167.63   $167.65   $167.60  
  Purchase #2 $230.86   13.311%   $261.5898   $261.59   $261.60   $261.60  
  Purchase #3 $47.71   8.276%   $51.6585   $51.66   $51.65   $51.70  
  Purchase #4 $39.90   3.795%   $41.4142   $41.41   $41.40   $41.40  
  Purchase #5 $21.83   4.109%   $22.727   $22.73   $22.75   $22.70  
  Purchase #6 $231.73   11.250%   $257.7996   $257.80   $257.80   $257.80  
  Purchase #7 $211.82   5.675%   $223.8408   $223.84   $223.85   $223.80  
  7 purchase totals = $942.67       $1,026.6612   $1,026.66   $1,026.70   $1,026.60