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 $151.95   7.260%   $162.9816   $162.98   $163.00   $163.00  
  Purchase #2 $21.95   13.578%   $24.9304   $24.93   $24.95   $24.90  
  Purchase #3 $79.91   5.841%   $84.5775   $84.58   $84.60   $84.60  
  Purchase #4 $155.98   8.420%   $169.1135   $169.11   $169.10   $169.10  
  Purchase #5 $49.77   9.690%   $54.5927   $54.59   $54.60   $54.60  
  Purchase #6 $31.57   13.708%   $35.8976   $35.90   $35.90   $35.90  
  Purchase #7 $225.97   9.381%   $247.1682   $247.17   $247.15   $247.20  
  7 purchase totals = $717.10       $779.2615   $779.26   $779.30   $779.30