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	$159.30	5.648%	$168.2973	$168.30	$168.30	$168.30
Purchase #2	$47.34	9.537%	$51.8548	$51.85	$51.85	$51.90
Purchase #3	$82.47	7.282%	$88.4755	$88.48	$88.50	$88.50
Purchase #4	$33.34	11.408%	$37.1434	$37.14	$37.15	$37.10
Purchase #5	$166.27	4.209%	$173.2683	$173.27	$173.25	$173.30
Purchase #6	$250.44	9.190%	$273.4554	$273.46	$273.45	$273.50
Purchase #7	$126.95	5.828%	$134.3486	$134.35	$134.35	$134.30
7 purchase totals =	$866.11		$926.8433	$926.85	$926.85	$926.90