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 $30.91   6.585%   $32.9454   $32.95   $32.95   $32.90  
  Purchase #2 $163.93   4.479%   $171.2724   $171.27   $171.25   $171.30  
  Purchase #3 $225.31   10.165%   $248.2128   $248.21   $248.20   $248.20  
  Purchase #4 $77.84   13.744%   $88.5383   $88.54   $88.55   $88.50  
  Purchase #5 $228.61   11.506%   $254.9139   $254.91   $254.90   $254.90  
  Purchase #6 $185.77   3.102%   $191.5326   $191.53   $191.55   $191.50  
  Purchase #7 $239.64   9.724%   $262.9426   $262.94   $262.95   $262.90  
  7 purchase totals = $1,152.01       $1,250.3580   $1,250.35   $1,250.35   $1,250.20