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	$89.67	11.193%	$99.7068	$99.71	$99.70	$99.70
Purchase #2	$57.71	5.165%	$60.6907	$60.69	$60.70	$60.70
Purchase #3	$19.25	9.521%	$21.0828	$21.08	$21.10	$21.10
Purchase #4	$98.55	12.713%	$111.0787	$111.08	$111.10	$111.10
Purchase #5	$144.50	7.755%	$155.706	$155.71	$155.70	$155.70
Purchase #6	$67.58	13.534%	$76.7263	$76.73	$76.75	$76.70
Purchase #7	$112.70	6.698%	$120.2486	$120.25	$120.25	$120.20
7 purchase totals =	$589.96		$645.2399	$645.25	$645.30	$645.20