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 $106.51   11.162%   $118.3986   $118.40   $118.40   $118.40  
  Purchase #2 $67.47   4.117%   $70.2477   $70.25   $70.25   $70.20  
  Purchase #3 $95.92   10.477%   $105.9695   $105.97   $105.95   $106.00  
  Purchase #4 $222.43   8.840%   $242.0928   $242.09   $242.10   $242.10  
  Purchase #5 $165.30   12.867%   $186.5692   $186.57   $186.55   $186.60  
  Purchase #6 $246.79   6.432%   $262.6635   $262.66   $262.65   $262.70  
  Purchase #7 $240.77   13.690%   $273.7314   $273.73   $273.75   $273.70  
  7 purchase totals = $1,145.19       $1,259.6727   $1,259.67   $1,259.65   $1,259.70