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	$50.55	9.595%	$55.4003	$55.40	$55.40	$55.40
Purchase #2	$243.70	12.324%	$273.7336	$273.73	$273.75	$273.70
Purchase #3	$158.62	12.500%	$178.4475	$178.45	$178.45	$178.40
Purchase #4	$206.32	11.207%	$229.4423	$229.44	$229.45	$229.40
Purchase #5	$89.54	7.627%	$96.3692	$96.37	$96.35	$96.40
Purchase #6	$104.54	6.272%	$111.0967	$111.10	$111.10	$111.10
Purchase #7	$144.89	8.333%	$156.9637	$156.96	$156.95	$157.00
7 purchase totals =	$998.16		$1,101.4533	$1,101.45	$1,101.45	$1,101.40