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	$49.40	7.531%	$53.1203	$53.12	$53.10	$53.10
Purchase #2	$181.92	13.301%	$206.1172	$206.12	$206.10	$206.10
Purchase #3	$123.48	13.257%	$139.8497	$139.85	$139.85	$139.80
Purchase #4	$243.27	9.336%	$265.9817	$265.98	$266.00	$266.00
Purchase #5	$110.89	3.523%	$114.7967	$114.80	$114.80	$114.80
Purchase #6	$178.73	4.717%	$187.1607	$187.16	$187.15	$187.20
Purchase #7	$10.95	4.150%	$11.4044	$11.40	$11.40	$11.40
7 purchase totals =	$898.64		$978.4307	$978.43	$978.40	$978.40