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 $23.96   11.322%   $26.6728   $26.67   $26.65   $26.70  
  Purchase #2 $246.26   8.311%   $266.7267   $266.73   $266.75   $266.70  
  Purchase #3 $135.25   12.292%   $151.8749   $151.87   $151.85   $151.90  
  Purchase #4 $217.84   3.546%   $225.5646   $225.56   $225.55   $225.60  
  Purchase #5 $146.50   13.858%   $166.802   $166.80   $166.80   $166.80  
  Purchase #6 $145.33   4.292%   $151.5676   $151.57   $151.55   $151.60  
  Purchase #7 $112.62   8.246%   $121.9066   $121.91   $121.90   $121.90  
  7 purchase totals = $1,027.76       $1,111.1152   $1,111.11   $1,111.05   $1,111.20