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 $211.84   3.157%   $218.5278   $218.53   $218.55   $218.50  
  Purchase #2 $112.44   6.124%   $119.3258   $119.33   $119.35   $119.30  
  Purchase #3 $231.58   10.283%   $255.3934   $255.39   $255.40   $255.40  
  Purchase #4 $174.30   10.673%   $192.903   $192.90   $192.90   $192.90  
  Purchase #5 $27.89   9.771%   $30.6151   $30.62   $30.60   $30.60  
  Purchase #6 $204.55   10.375%   $225.7721   $225.77   $225.75   $225.80  
  Purchase #7 $60.60   10.863%   $67.183   $67.18   $67.20   $67.20  
  7 purchase totals = $1,023.20       $1,109.7202   $1,109.72   $1,109.75   $1,109.70