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	$82.80	13.422%	$93.9134	$93.91	$93.90	$93.90
Purchase #2	$49.55	13.528%	$56.2531	$56.25	$56.25	$56.30
Purchase #3	$10.28	5.865%	$10.8829	$10.88	$10.90	$10.90
Purchase #4	$197.46	12.872%	$222.8771	$222.88	$222.90	$222.90
Purchase #5	$129.51	6.335%	$137.7145	$137.71	$137.70	$137.70
Purchase #6	$21.40	4.223%	$22.3037	$22.30	$22.30	$22.30
Purchase #7	$168.83	12.180%	$189.3935	$189.39	$189.40	$189.40
7 purchase totals =	$659.83		$733.3382	$733.32	$733.35	$733.40