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	$105.33	10.272%	$116.1495	$116.15	$116.15	$116.10
Purchase #2	$222.65	9.376%	$243.5257	$243.53	$243.55	$243.50
Purchase #3	$95.74	13.220%	$108.3968	$108.40	$108.40	$108.40
Purchase #4	$181.91	9.861%	$199.8481	$199.85	$199.85	$199.80
Purchase #5	$65.52	7.567%	$70.4779	$70.48	$70.50	$70.50
Purchase #6	$37.55	12.820%	$42.3639	$42.36	$42.35	$42.40
Purchase #7	$19.99	5.821%	$21.1536	$21.15	$21.15	$21.20
7 purchase totals =	$728.69		$801.9155	$801.92	$801.95	$801.90