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	$159.81	7.171%	$171.27	$171.27	$171.25	$171.30
Purchase #2	$81.76	10.403%	$90.2655	$90.27	$90.25	$90.30
Purchase #3	$165.96	6.735%	$177.1374	$177.14	$177.15	$177.10
Purchase #4	$66.68	12.865%	$75.2584	$75.26	$75.25	$75.30
Purchase #5	$51.52	9.251%	$56.2861	$56.29	$56.30	$56.30
Purchase #6	$71.84	9.548%	$78.6993	$78.70	$78.70	$78.70
Purchase #7	$36.25	4.496%	$37.8798	$37.88	$37.90	$37.90
7 purchase totals =	$633.82		$686.7965	$686.81	$686.80	$686.90