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	$44.73	13.277%	$50.6688	$50.67	$50.65	$50.70
Purchase #2	$242.74	12.506%	$273.0971	$273.10	$273.10	$273.10
Purchase #3	$99.57	6.123%	$105.6667	$105.67	$105.65	$105.70
Purchase #4	$55.97	8.513%	$60.7347	$60.73	$60.75	$60.70
Purchase #5	$196.78	9.200%	$214.8838	$214.88	$214.90	$214.90
Purchase #6	$232.97	4.557%	$243.5864	$243.59	$243.60	$243.60
Purchase #7	$186.56	5.314%	$196.4738	$196.47	$196.45	$196.50
7 purchase totals =	$1,059.32		$1,145.1113	$1,145.11	$1,145.10	$1,145.20