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 $201.88   10.498%   $223.0734   $223.07   $223.05   $223.10  
  Purchase #2 $80.60   11.234%   $89.6546   $89.65   $89.65   $89.70  
  Purchase #3 $17.88   4.636%   $18.7089   $18.71   $18.70   $18.70  
  Purchase #4 $218.91   11.606%   $244.3167   $244.32   $244.30   $244.30  
  Purchase #5 $142.93   4.157%   $148.8716   $148.87   $148.85   $148.90  
  Purchase #6 $199.33   4.835%   $208.9676   $208.97   $208.95   $209.00  
  Purchase #7 $154.39   8.604%   $167.6737   $167.67   $167.65   $167.70  
  7 purchase totals = $1,015.92       $1,101.2665   $1,101.26   $1,101.15   $1,101.40