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 $23.48   12.116%   $26.3248   $26.32   $26.30   $26.30  
  Purchase #2 $242.94   12.379%   $273.0135   $273.01   $273.00   $273.00  
  Purchase #3 $120.38   13.558%   $136.7011   $136.70   $136.70   $136.70  
  Purchase #4 $155.70   7.428%   $167.2654   $167.27   $167.25   $167.30  
  Purchase #5 $65.98   5.327%   $69.4948   $69.49   $69.50   $69.50  
  Purchase #6 $170.53   3.546%   $176.577   $176.58   $176.60   $176.60  
  Purchase #7 $165.72   11.660%   $185.043   $185.04   $185.05   $185.00  
  7 purchase totals = $944.73       $1,034.4196   $1,034.41   $1,034.40   $1,034.40