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	$18.61	8.394%	$20.1721	$20.17	$20.15	$20.20
Purchase #2	$38.94	6.540%	$41.4867	$41.49	$41.50	$41.50
Purchase #3	$206.89	13.415%	$234.6443	$234.64	$234.65	$234.60
Purchase #4	$194.94	4.516%	$203.7435	$203.74	$203.75	$203.70
Purchase #5	$85.30	6.608%	$90.9366	$90.94	$90.95	$90.90
Purchase #6	$195.29	13.786%	$222.2127	$222.21	$222.20	$222.20
Purchase #7	$42.32	6.780%	$45.1893	$45.19	$45.20	$45.20
7 purchase totals =	$782.29		$858.3852	$858.38	$858.40	$858.30