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 $147.50   10.242%   $162.607   $162.61   $162.60   $162.60  
  Purchase #2 $29.74   3.406%   $30.7529   $30.75   $30.75   $30.80  
  Purchase #3 $58.72   10.526%   $64.9009   $64.90   $64.90   $64.90  
  Purchase #4 $150.48   9.189%   $164.3076   $164.31   $164.30   $164.30  
  Purchase #5 $127.51   6.774%   $136.1475   $136.15   $136.15   $136.10  
  Purchase #6 $27.28   8.633%   $29.6351   $29.64   $29.65   $29.60  
  Purchase #7 $237.64   8.485%   $257.8038   $257.80   $257.80   $257.80  
  7 purchase totals = $778.87       $846.1548   $846.16   $846.15   $846.10