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	$100.61	10.362%	$111.0352	$111.04	$111.05	$111.00
Purchase #2	$91.48	10.715%	$101.2821	$101.28	$101.30	$101.30
Purchase #3	$229.40	6.392%	$244.0632	$244.06	$244.05	$244.10
Purchase #4	$226.91	3.778%	$235.4827	$235.48	$235.50	$235.50
Purchase #5	$26.76	7.557%	$28.7823	$28.78	$28.80	$28.80
Purchase #6	$45.58	4.280%	$47.5308	$47.53	$47.55	$47.50
Purchase #7	$137.54	10.272%	$151.6681	$151.67	$151.65	$151.70
7 purchase totals =	$858.28		$919.8444	$919.84	$919.90	$919.90