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 $63.75   13.241%   $72.1911   $72.19   $72.20   $72.20  
  Purchase #2 $195.77   8.128%   $211.6822   $211.68   $211.70   $211.70  
  Purchase #3 $247.40   6.773%   $264.1564   $264.16   $264.15   $264.20  
  Purchase #4 $203.50   12.199%   $228.325   $228.33   $228.35   $228.30  
  Purchase #5 $135.47   7.521%   $145.6587   $145.66   $145.65   $145.70  
  Purchase #6 $231.67   3.382%   $239.5051   $239.51   $239.50   $239.50  
  Purchase #7 $233.77   5.511%   $246.6531   $246.65   $246.65   $246.70  
  7 purchase totals = $1,311.33       $1,408.1716   $1,408.18   $1,408.20   $1,408.30