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 $88.58   11.242%   $98.5382   $98.54   $98.55   $98.50  
  Purchase #2 $154.30   10.426%   $170.3873   $170.39   $170.40   $170.40  
  Purchase #3 $76.43   13.149%   $86.4798   $86.48   $86.50   $86.50  
  Purchase #4 $96.25   8.147%   $104.0915   $104.09   $104.10   $104.10  
  Purchase #5 $215.86   7.424%   $231.8854   $231.89   $231.90   $231.90  
  Purchase #6 $94.96   7.850%   $102.4144   $102.41   $102.40   $102.40  
  Purchase #7 $180.62   3.772%   $187.433   $187.43   $187.45   $187.40  
  7 purchase totals = $907.00       $981.2296   $981.23   $981.30   $981.20