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 $218.75   3.619%   $226.6666   $226.67   $226.65   $226.70  
  Purchase #2 $64.66   13.445%   $73.3535   $73.35   $73.35   $73.40  
  Purchase #3 $59.90   5.189%   $63.0082   $63.01   $63.00   $63.00  
  Purchase #4 $42.27   12.135%   $47.3995   $47.40   $47.40   $47.40  
  Purchase #5 $109.96   12.149%   $123.319   $123.32   $123.30   $123.30  
  Purchase #6 $246.40   12.675%   $277.6312   $277.63   $277.65   $277.60  
  Purchase #7 $115.26   12.224%   $129.3494   $129.35   $129.35   $129.30  
  7 purchase totals = $857.20       $940.7274   $940.73   $940.70   $940.70