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	$180.67	4.314%	$188.4641	$188.46	$188.45	$188.50
Purchase #2	$171.46	6.214%	$182.1145	$182.11	$182.10	$182.10
Purchase #3	$79.30	4.211%	$82.6393	$82.64	$82.65	$82.60
Purchase #4	$132.39	10.860%	$146.7676	$146.77	$146.75	$146.80
Purchase #5	$155.95	8.573%	$169.3196	$169.32	$169.30	$169.30
Purchase #6	$32.39	3.547%	$33.5389	$33.54	$33.55	$33.50
Purchase #7	$173.93	11.677%	$194.2398	$194.24	$194.25	$194.20
7 purchase totals =	$926.09		$997.0838	$997.08	$997.05	$997.00