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	$34.63	9.793%	$38.0213	$38.02	$38.00	$38.00
Purchase #2	$35.77	12.148%	$40.1153	$40.12	$40.10	$40.10
Purchase #3	$128.49	9.118%	$140.2057	$140.21	$140.20	$140.20
Purchase #4	$64.42	11.234%	$71.6569	$71.66	$71.65	$71.70
Purchase #5	$216.72	11.103%	$240.7824	$240.78	$240.80	$240.80
Purchase #6	$191.59	10.621%	$211.9388	$211.94	$211.95	$211.90
Purchase #7	$154.55	10.828%	$171.2847	$171.28	$171.30	$171.30
7 purchase totals =	$826.17		$914.0051	$914.01	$914.00	$914.00