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 $67.64   11.123%   $75.1636   $75.16   $75.15   $75.20  
  Purchase #2 $187.43   12.238%   $210.3677   $210.37   $210.35   $210.40  
  Purchase #3 $200.98   8.596%   $218.2562   $218.26   $218.25   $218.30  
  Purchase #4 $234.72   7.652%   $252.6808   $252.68   $252.70   $252.70  
  Purchase #5 $117.62   13.437%   $133.4246   $133.42   $133.40   $133.40  
  Purchase #6 $248.68   13.164%   $281.4162   $281.42   $281.40   $281.40  
  Purchase #7 $190.91   4.458%   $199.4208   $199.42   $199.40   $199.40  
  7 purchase totals = $1,247.98       $1,370.7299   $1,370.73   $1,370.65   $1,370.80