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 $77.40   13.142%   $87.5719   $87.57   $87.55   $87.60  
  Purchase #2 $221.37   11.340%   $246.4734   $246.47   $246.45   $246.50  
  Purchase #3 $110.84   3.311%   $114.5099   $114.51   $114.50   $114.50  
  Purchase #4 $26.91   12.393%   $30.245   $30.25   $30.25   $30.20  
  Purchase #5 $87.63   6.277%   $93.1305   $93.13   $93.15   $93.10  
  Purchase #6 $192.59   8.785%   $209.509   $209.51   $209.50   $209.50  
  Purchase #7 $99.71   6.144%   $105.8362   $105.84   $105.85   $105.80  
  7 purchase totals = $816.45       $887.2759   $887.28   $887.25   $887.20