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	$230.33	6.544%	$245.4028	$245.40	$245.40	$245.40
Purchase #2	$143.43	3.368%	$148.2607	$148.26	$148.25	$148.30
Purchase #3	$77.91	9.803%	$85.5475	$85.55	$85.55	$85.50
Purchase #4	$169.63	9.832%	$186.308	$186.31	$186.30	$186.30
Purchase #5	$157.47	11.335%	$175.3192	$175.32	$175.30	$175.30
Purchase #6	$158.41	8.687%	$172.1711	$172.17	$172.15	$172.20
Purchase #7	$162.82	9.831%	$178.8268	$178.83	$178.85	$178.80
7 purchase totals =	$1,100.00		$1,191.8361	$1,191.84	$1,191.80	$1,191.80