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	$83.75	6.345%	$89.0639	$89.06	$89.05	$89.10
Purchase #2	$20.75	3.140%	$21.4016	$21.40	$21.40	$21.40
Purchase #3	$120.29	6.233%	$127.7877	$127.79	$127.80	$127.80
Purchase #4	$91.66	3.363%	$94.7425	$94.74	$94.75	$94.70
Purchase #5	$221.93	11.284%	$246.9726	$246.97	$246.95	$247.00
Purchase #6	$141.90	4.302%	$148.0045	$148.00	$148.00	$148.00
Purchase #7	$172.83	10.459%	$190.9063	$190.91	$190.90	$190.90
7 purchase totals =	$853.11		$918.8791	$918.87	$918.85	$918.90