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	$98.29	6.175%	$104.3594	$104.36	$104.35	$104.40
Purchase #2	$111.58	4.820%	$116.9582	$116.96	$116.95	$117.00
Purchase #3	$62.81	7.323%	$67.4096	$67.41	$67.40	$67.40
Purchase #4	$17.56	4.166%	$18.2915	$18.29	$18.30	$18.30
Purchase #5	$115.84	6.204%	$123.0267	$123.03	$123.05	$123.00
Purchase #6	$215.44	7.759%	$232.156	$232.16	$232.15	$232.20
Purchase #7	$123.38	3.498%	$127.6958	$127.70	$127.70	$127.70
7 purchase totals =	$744.90		$789.8972	$789.91	$789.90	$790.00