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	$123.67	6.488%	$131.6937	$131.69	$131.70	$131.70
Purchase #2	$215.56	13.134%	$243.8717	$243.87	$243.85	$243.90
Purchase #3	$93.40	6.416%	$99.3925	$99.39	$99.40	$99.40
Purchase #4	$224.44	13.539%	$254.8269	$254.83	$254.85	$254.80
Purchase #5	$126.29	7.779%	$136.1141	$136.11	$136.10	$136.10
Purchase #6	$111.87	5.259%	$117.7532	$117.75	$117.75	$117.80
Purchase #7	$108.82	5.488%	$114.792	$114.79	$114.80	$114.80
7 purchase totals =	$1,004.05		$1,098.4441	$1,098.43	$1,098.45	$1,098.50