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	$49.45	3.754%	$51.3064	$51.31	$51.30	$51.30
Purchase #2	$140.76	8.577%	$152.833	$152.83	$152.85	$152.80
Purchase #3	$189.40	13.526%	$215.0182	$215.02	$215.00	$215.00
Purchase #4	$224.93	13.283%	$254.8075	$254.81	$254.80	$254.80
Purchase #5	$30.40	4.595%	$31.7969	$31.80	$31.80	$31.80
Purchase #6	$68.92	5.605%	$72.783	$72.78	$72.80	$72.80
Purchase #7	$189.81	13.407%	$215.2578	$215.26	$215.25	$215.30
7 purchase totals =	$893.67		$993.8028	$993.81	$993.80	$993.80