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 $65.76   8.869%   $71.5923   $71.59   $71.60   $71.60  
  Purchase #2 $151.94   10.299%   $167.5883   $167.59   $167.60   $167.60  
  Purchase #3 $201.73   8.685%   $219.2503   $219.25   $219.25   $219.30  
  Purchase #4 $35.27   4.270%   $36.776   $36.78   $36.80   $36.80  
  Purchase #5 $68.34   9.298%   $74.6943   $74.69   $74.70   $74.70  
  Purchase #6 $213.99   8.268%   $231.6827   $231.68   $231.70   $231.70  
  Purchase #7 $8.34   3.731%   $8.6512   $8.65   $8.65   $8.70  
  7 purchase totals = $745.37       $810.2351   $810.23   $810.30   $810.40