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 $97.83   9.182%   $106.8128   $106.81   $106.80   $106.80  
  Purchase #2 $215.83   3.408%   $223.1855   $223.19   $223.20   $223.20  
  Purchase #3 $157.80   6.240%   $167.6467   $167.65   $167.65   $167.60  
  Purchase #4 $239.49   8.238%   $259.2192   $259.22   $259.20   $259.20  
  Purchase #5 $23.51   9.527%   $25.7498   $25.75   $25.75   $25.70  
  Purchase #6 $116.69   11.627%   $130.2575   $130.26   $130.25   $130.30  
  Purchase #7 $94.64   7.154%   $101.4105   $101.41   $101.40   $101.40  
  7 purchase totals = $945.79       $1,014.2820   $1,014.29   $1,014.25   $1,014.20