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 $53.51   7.708%   $57.6346   $57.63   $57.65   $57.60  
  Purchase #2 $151.41   10.125%   $166.7403   $166.74   $166.75   $166.70  
  Purchase #3 $109.79   5.265%   $115.5704   $115.57   $115.55   $115.60  
  Purchase #4 $239.87   6.144%   $254.6076   $254.61   $254.60   $254.60  
  Purchase #5 $79.53   4.834%   $83.3745   $83.37   $83.35   $83.40  
  Purchase #6 $203.94   5.864%   $215.899   $215.90   $215.90   $215.90  
  Purchase #7 $229.58   12.327%   $257.8803   $257.88   $257.90   $257.90  
  7 purchase totals = $1,067.63       $1,151.7067   $1,151.70   $1,151.70   $1,151.70