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	$84.64	5.755%	$89.511	$89.51	$89.50	$89.50
Purchase #2	$104.91	10.727%	$116.1637	$116.16	$116.15	$116.20
Purchase #3	$90.71	6.760%	$96.842	$96.84	$96.85	$96.80
Purchase #4	$126.89	5.869%	$134.3372	$134.34	$134.35	$134.30
Purchase #5	$167.34	7.525%	$179.9323	$179.93	$179.95	$179.90
Purchase #6	$176.73	4.766%	$185.153	$185.15	$185.15	$185.20
Purchase #7	$21.99	8.401%	$23.8374	$23.84	$23.85	$23.80
7 purchase totals =	$773.21		$825.7766	$825.77	$825.80	$825.70