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 $56.62   13.619%   $64.3311   $64.33   $64.35   $64.30  
  Purchase #2 $131.63   12.245%   $147.7481   $147.75   $147.75   $147.70  
  Purchase #3 $208.41   12.721%   $234.9218   $234.92   $234.90   $234.90  
  Purchase #4 $225.27   11.632%   $251.4734   $251.47   $251.45   $251.50  
  Purchase #5 $226.95   8.720%   $246.74   $246.74   $246.75   $246.70  
  Purchase #6 $158.66   3.573%   $164.3289   $164.33   $164.35   $164.30  
  Purchase #7 $178.74   3.574%   $185.1282   $185.13   $185.15   $185.10  
  7 purchase totals = $1,186.28       $1,294.6715   $1,294.67   $1,294.70   $1,294.50