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 $23.52   11.304%   $26.1787   $26.18   $26.20   $26.20  
  Purchase #2 $195.91   9.667%   $214.8486   $214.85   $214.85   $214.80  
  Purchase #3 $240.34   8.137%   $259.8965   $259.90   $259.90   $259.90  
  Purchase #4 $75.64   8.498%   $82.0679   $82.07   $82.05   $82.10  
  Purchase #5 $87.63   4.308%   $91.4051   $91.41   $91.40   $91.40  
  Purchase #6 $223.73   6.673%   $238.6595   $238.66   $238.65   $238.70  
  Purchase #7 $218.83   5.579%   $231.0385   $231.04   $231.05   $231.00  
  7 purchase totals = $1,065.60       $1,144.0948   $1,144.11   $1,144.10   $1,144.10