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	$26.40	4.401%	$27.5619	$27.56	$27.55	$27.60
Purchase #2	$45.44	10.649%	$50.2789	$50.28	$50.30	$50.30
Purchase #3	$154.75	3.738%	$160.5346	$160.53	$160.55	$160.50
Purchase #4	$137.51	4.341%	$143.4793	$143.48	$143.50	$143.50
Purchase #5	$247.82	11.639%	$276.6638	$276.66	$276.65	$276.70
Purchase #6	$84.25	8.829%	$91.6884	$91.69	$91.70	$91.70
Purchase #7	$80.97	10.604%	$89.5561	$89.56	$89.55	$89.60
7 purchase totals =	$777.14		$839.7630	$839.76	$839.80	$839.90