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 $193.68   7.405%   $208.022   $208.02   $208.00   $208.00  
  Purchase #2 $80.89   3.826%   $83.9849   $83.98   $84.00   $84.00  
  Purchase #3 $233.49   12.586%   $262.8771   $262.88   $262.90   $262.90  
  Purchase #4 $214.35   8.321%   $232.1861   $232.19   $232.20   $232.20  
  Purchase #5 $94.89   9.402%   $103.8116   $103.81   $103.80   $103.80  
  Purchase #6 $191.90   13.609%   $218.0157   $218.02   $218.00   $218.00  
  Purchase #7 $246.48   9.481%   $269.8488   $269.85   $269.85   $269.80  
  7 purchase totals = $1,255.68       $1,378.7462   $1,378.75   $1,378.75   $1,378.70