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	$72.85	12.403%	$81.8856	$81.89	$81.90	$81.90
Purchase #2	$160.29	12.362%	$180.105	$180.11	$180.10	$180.10
Purchase #3	$25.95	7.237%	$27.828	$27.83	$27.85	$27.80
Purchase #4	$56.66	3.426%	$58.6012	$58.60	$58.60	$58.60
Purchase #5	$170.31	7.251%	$182.6592	$182.66	$182.65	$182.70
Purchase #6	$247.90	4.501%	$259.058	$259.06	$259.05	$259.10
Purchase #7	$49.57	9.829%	$54.4422	$54.44	$54.45	$54.40
7 purchase totals =	$783.53		$844.5792	$844.59	$844.60	$844.60