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 $84.54   11.237%   $94.0398   $94.04   $94.05   $94.00  
  Purchase #2 $92.78   13.388%   $105.2014   $105.20   $105.20   $105.20  
  Purchase #3 $86.32   3.828%   $89.6243   $89.62   $89.60   $89.60  
  Purchase #4 $14.59   8.184%   $15.784   $15.78   $15.80   $15.80  
  Purchase #5 $226.54   5.563%   $239.1424   $239.14   $239.15   $239.10  
  Purchase #6 $150.32   8.841%   $163.6098   $163.61   $163.60   $163.60  
  Purchase #7 $235.35   8.855%   $256.1902   $256.19   $256.20   $256.20  
  7 purchase totals = $890.44       $963.5919   $963.58   $963.60   $963.50