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	$206.52	13.258%	$233.9004	$233.90	$233.90	$233.90
Purchase #2	$40.57	5.512%	$42.8062	$42.81	$42.80	$42.80
Purchase #3	$56.79	5.346%	$59.826	$59.83	$59.85	$59.80
Purchase #4	$240.47	10.120%	$264.8056	$264.81	$264.80	$264.80
Purchase #5	$228.49	11.309%	$254.3299	$254.33	$254.35	$254.30
Purchase #6	$195.37	4.687%	$204.527	$204.53	$204.55	$204.50
Purchase #7	$212.64	10.483%	$234.9311	$234.93	$234.95	$234.90
7 purchase totals =	$1,180.85		$1,295.1262	$1,295.14	$1,295.20	$1,295.00