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	$191.34	7.318%	$205.3423	$205.34	$205.35	$205.30
Purchase #2	$136.83	3.830%	$142.0706	$142.07	$142.05	$142.10
Purchase #3	$105.67	12.176%	$118.5364	$118.54	$118.55	$118.50
Purchase #4	$62.77	3.735%	$65.1145	$65.11	$65.10	$65.10
Purchase #5	$247.67	10.648%	$274.0419	$274.04	$274.05	$274.00
Purchase #6	$54.74	4.231%	$57.056	$57.06	$57.05	$57.10
Purchase #7	$138.40	8.680%	$150.4131	$150.41	$150.40	$150.40
7 purchase totals =	$937.42		$1,012.5748	$1,012.57	$1,012.55	$1,012.50