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	$57.78	11.502%	$64.4259	$64.43	$64.45	$64.40
Purchase #2	$98.83	12.612%	$111.2944	$111.29	$111.30	$111.30
Purchase #3	$196.74	9.299%	$215.0349	$215.03	$215.05	$215.00
Purchase #4	$39.83	8.334%	$43.1494	$43.15	$43.15	$43.10
Purchase #5	$99.34	12.482%	$111.7396	$111.74	$111.75	$111.70
Purchase #6	$18.93	13.251%	$21.4384	$21.44	$21.45	$21.40
Purchase #7	$176.52	4.669%	$184.7617	$184.76	$184.75	$184.80
7 purchase totals =	$687.97		$751.8443	$751.84	$751.90	$751.70