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	$41.72	12.361%	$46.877	$46.88	$46.90	$46.90
Purchase #2	$242.67	8.132%	$262.4039	$262.40	$262.40	$262.40
Purchase #3	$248.28	12.679%	$279.7594	$279.76	$279.75	$279.80
Purchase #4	$180.89	9.747%	$198.5213	$198.52	$198.50	$198.50
Purchase #5	$33.89	12.479%	$38.1191	$38.12	$38.10	$38.10
Purchase #6	$139.36	7.226%	$149.4302	$149.43	$149.45	$149.40
Purchase #7	$39.65	13.159%	$44.8675	$44.87	$44.85	$44.90
7 purchase totals =	$926.46		$1,019.9784	$1,019.98	$1,019.95	$1,020.00