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	$142.40	8.268%	$154.1736	$154.17	$154.15	$154.20
Purchase #2	$213.76	13.498%	$242.6133	$242.61	$242.60	$242.60
Purchase #3	$35.41	8.542%	$38.4347	$38.43	$38.45	$38.40
Purchase #4	$172.88	4.787%	$181.1558	$181.16	$181.15	$181.20
Purchase #5	$73.31	8.619%	$79.6286	$79.63	$79.65	$79.60
Purchase #6	$64.27	9.674%	$70.4875	$70.49	$70.50	$70.50
Purchase #7	$82.90	7.334%	$88.9799	$88.98	$89.00	$89.00
7 purchase totals =	$784.93		$855.4734	$855.47	$855.50	$855.50