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 $195.42   10.362%   $215.6694   $215.67   $215.65   $215.70  
  Purchase #2 $233.80   12.798%   $263.7217   $263.72   $263.70   $263.70  
  Purchase #3 $108.25   9.346%   $118.367   $118.37   $118.35   $118.40  
  Purchase #4 $215.30   12.829%   $242.9208   $242.92   $242.90   $242.90  
  Purchase #5 $239.70   9.777%   $263.1355   $263.14   $263.15   $263.10  
  Purchase #6 $63.68   8.516%   $69.103   $69.10   $69.10   $69.10  
  Purchase #7 $228.74   11.351%   $254.7043   $254.70   $254.70   $254.70  
  7 purchase totals = $1,284.89       $1,427.6217   $1,427.62   $1,427.55   $1,427.60