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 $79.47   8.504%   $86.2281   $86.23   $86.25   $86.20  
  Purchase #2 $244.62   13.177%   $276.8536   $276.85   $276.85   $276.90  
  Purchase #3 $166.48   4.258%   $173.5687   $173.57   $173.55   $173.60  
  Purchase #4 $212.82   4.766%   $222.963   $222.96   $222.95   $223.00  
  Purchase #5 $101.84   12.463%   $114.5323   $114.53   $114.55   $114.50  
  Purchase #6 $106.88   9.341%   $116.8637   $116.86   $116.85   $116.90  
  Purchase #7 $149.74   13.631%   $170.1511   $170.15   $170.15   $170.20  
  7 purchase totals = $1,061.85       $1,161.1605   $1,161.15   $1,161.15   $1,161.30