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 $82.34   7.581%   $88.5822   $88.58   $88.60   $88.60  
  Purchase #2 $237.64   6.380%   $252.8014   $252.80   $252.80   $252.80  
  Purchase #3 $159.51   6.336%   $169.6166   $169.62   $169.60   $169.60  
  Purchase #4 $53.87   7.795%   $58.0692   $58.07   $58.05   $58.10  
  Purchase #5 $5.90   13.584%   $6.7015   $6.70   $6.70   $6.70  
  Purchase #6 $186.44   11.647%   $208.1547   $208.15   $208.15   $208.20  
  Purchase #7 $27.25   9.301%   $29.7845   $29.78   $29.80   $29.80  
  7 purchase totals = $752.95       $813.7101   $813.70   $813.70   $813.80