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 $237.69   10.474%   $262.5857   $262.59   $262.60   $262.60  
  Purchase #2 $78.41   12.382%   $88.1187   $88.12   $88.10   $88.10  
  Purchase #3 $226.94   9.666%   $248.876   $248.88   $248.90   $248.90  
  Purchase #4 $88.94   3.166%   $91.7558   $91.76   $91.75   $91.80  
  Purchase #5 $133.46   8.865%   $145.2912   $145.29   $145.30   $145.30  
  Purchase #6 $221.62   12.405%   $249.112   $249.11   $249.10   $249.10  
  Purchase #7 $163.41   10.333%   $180.2952   $180.30   $180.30   $180.30  
  7 purchase totals = $1,150.47       $1,266.0346   $1,266.05   $1,266.05   $1,266.10