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	$16.56	12.656%	$18.6558	$18.66	$18.65	$18.70
Purchase #2	$41.89	4.660%	$43.8421	$43.84	$43.85	$43.80
Purchase #3	$75.81	7.267%	$81.3191	$81.32	$81.30	$81.30
Purchase #4	$47.73	9.538%	$52.2825	$52.28	$52.30	$52.30
Purchase #5	$43.30	6.668%	$46.1872	$46.19	$46.20	$46.20
Purchase #6	$76.52	7.355%	$82.148	$82.15	$82.15	$82.10
Purchase #7	$239.27	10.553%	$264.5202	$264.52	$264.50	$264.50
7 purchase totals =	$541.08		$588.9549	$588.96	$588.95	$588.90