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 $23.46   12.833%   $26.4706   $26.47   $26.45   $26.50  
  Purchase #2 $94.94   8.394%   $102.9093   $102.91   $102.90   $102.90  
  Purchase #3 $245.26   9.780%   $269.2464   $269.25   $269.25   $269.20  
  Purchase #4 $107.94   5.112%   $113.4579   $113.46   $113.45   $113.50  
  Purchase #5 $163.63   10.758%   $181.2333   $181.23   $181.25   $181.20  
  Purchase #6 $165.50   10.847%   $183.4518   $183.45   $183.45   $183.50  
  Purchase #7 $206.95   4.551%   $216.3683   $216.37   $216.35   $216.40  
  7 purchase totals = $1,007.68       $1,093.1376   $1,093.14   $1,093.10   $1,093.20