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 $214.75   7.662%   $231.2041   $231.20   $231.20   $231.20  
  Purchase #2 $110.87   5.417%   $116.8758   $116.88   $116.90   $116.90  
  Purchase #3 $143.51   9.642%   $157.3472   $157.35   $157.35   $157.30  
  Purchase #4 $35.30   7.721%   $38.0255   $38.03   $38.05   $38.00  
  Purchase #5 $94.82   5.310%   $99.8549   $99.85   $99.85   $99.90  
  Purchase #6 $44.79   8.509%   $48.6012   $48.60   $48.60   $48.60  
  Purchase #7 $234.61   13.787%   $266.9557   $266.96   $266.95   $267.00  
  7 purchase totals = $878.65       $958.8644   $958.87   $958.90   $958.90