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 $214.88   12.404%   $241.5337   $241.53   $241.55   $241.50  
  Purchase #2 $96.44   11.551%   $107.5798   $107.58   $107.60   $107.60  
  Purchase #3 $178.54   3.487%   $184.7657   $184.77   $184.75   $184.80  
  Purchase #4 $165.39   6.639%   $176.3702   $176.37   $176.35   $176.40  
  Purchase #5 $153.28   8.300%   $166.0022   $166.00   $166.00   $166.00  
  Purchase #6 $193.92   8.221%   $209.8622   $209.86   $209.85   $209.90  
  Purchase #7 $145.27   6.189%   $154.2608   $154.26   $154.25   $154.30  
  7 purchase totals = $1,147.72       $1,240.3746   $1,240.37   $1,240.35   $1,240.50