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	$57.82	4.634%	$60.4994	$60.50	$60.50	$60.50
Purchase #2	$242.68	12.591%	$273.2358	$273.24	$273.25	$273.20
Purchase #3	$79.33	4.463%	$82.8705	$82.87	$82.85	$82.90
Purchase #4	$60.68	8.104%	$65.5975	$65.60	$65.60	$65.60
Purchase #5	$234.44	12.305%	$263.2878	$263.29	$263.30	$263.30
Purchase #6	$223.85	13.710%	$254.5398	$254.54	$254.55	$254.50
Purchase #7	$88.89	11.654%	$99.2492	$99.25	$99.25	$99.20
7 purchase totals =	$987.69		$1,099.2800	$1,099.29	$1,099.30	$1,099.20