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 $204.68   6.747%   $218.4898   $218.49   $218.50   $218.50  
  Purchase #2 $95.32   13.486%   $108.1749   $108.17   $108.15   $108.20  
  Purchase #3 $49.30   9.371%   $53.9199   $53.92   $53.90   $53.90  
  Purchase #4 $229.40   12.545%   $258.1782   $258.18   $258.20   $258.20  
  Purchase #5 $231.89   7.238%   $248.6742   $248.67   $248.65   $248.70  
  Purchase #6 $237.29   13.663%   $269.7109   $269.71   $269.70   $269.70  
  Purchase #7 $78.87   11.166%   $87.6766   $87.68   $87.70   $87.70  
  7 purchase totals = $1,126.75       $1,244.8245   $1,244.82   $1,244.80   $1,244.90