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 $80.52   3.262%   $83.1466   $83.15   $83.15   $83.10  
  Purchase #2 $248.85   11.409%   $277.2413   $277.24   $277.25   $277.20  
  Purchase #3 $60.40   11.324%   $67.2397   $67.24   $67.25   $67.20  
  Purchase #4 $239.98   5.321%   $252.7493   $252.75   $252.75   $252.70  
  Purchase #5 $165.98   5.156%   $174.5379   $174.54   $174.55   $174.50  
  Purchase #6 $71.51   9.862%   $78.5623   $78.56   $78.55   $78.60  
  Purchase #7 $221.69   8.783%   $241.161   $241.16   $241.15   $241.20  
  7 purchase totals = $1,088.93       $1,174.6381   $1,174.64   $1,174.65   $1,174.50