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	$85.32	7.623%	$91.8239	$91.82	$91.80	$91.80
Purchase #2	$97.46	8.757%	$105.9946	$105.99	$106.00	$106.00
Purchase #3	$18.61	3.785%	$19.3144	$19.31	$19.30	$19.30
Purchase #4	$127.45	7.489%	$136.9947	$136.99	$137.00	$137.00
Purchase #5	$85.47	6.133%	$90.7119	$90.71	$90.70	$90.70
Purchase #6	$148.96	4.595%	$155.8047	$155.80	$155.80	$155.80
Purchase #7	$40.92	3.298%	$42.2695	$42.27	$42.25	$42.30
7 purchase totals =	$604.19		$642.9137	$642.89	$642.85	$642.90