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	$59.45	6.251%	$63.1662	$63.17	$63.15	$63.20
Purchase #2	$117.89	12.260%	$132.3433	$132.34	$132.35	$132.30
Purchase #3	$53.62	11.375%	$59.7193	$59.72	$59.70	$59.70
Purchase #4	$196.94	7.556%	$211.8208	$211.82	$211.80	$211.80
Purchase #5	$85.67	5.428%	$90.3202	$90.32	$90.30	$90.30
Purchase #6	$147.35	5.665%	$155.6974	$155.70	$155.70	$155.70
Purchase #7	$189.60	5.677%	$200.3636	$200.36	$200.35	$200.40
7 purchase totals =	$850.52		$913.4308	$913.43	$913.35	$913.40