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 $135.58   6.173%   $143.9494   $143.95   $143.95   $143.90  
  Purchase #2 $236.85   10.823%   $262.4843   $262.48   $262.50   $262.50  
  Purchase #3 $245.53   9.495%   $268.8431   $268.84   $268.85   $268.80  
  Purchase #4 $233.70   3.523%   $241.9333   $241.93   $241.95   $241.90  
  Purchase #5 $55.93   11.709%   $62.4788   $62.48   $62.50   $62.50  
  Purchase #6 $144.65   9.168%   $157.9115   $157.91   $157.90   $157.90  
  Purchase #7 $194.81   12.371%   $218.9099   $218.91   $218.90   $218.90  
  7 purchase totals = $1,247.05       $1,356.5103   $1,356.50   $1,356.55   $1,356.40