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	$71.30	10.111%	$78.5091	$78.51	$78.50	$78.50
Purchase #2	$158.69	5.459%	$167.3529	$167.35	$167.35	$167.40
Purchase #3	$185.83	10.806%	$205.9108	$205.91	$205.90	$205.90
Purchase #4	$162.69	11.773%	$181.8435	$181.84	$181.85	$181.80
Purchase #5	$64.46	7.683%	$69.4125	$69.41	$69.40	$69.40
Purchase #6	$87.56	7.316%	$93.9659	$93.97	$93.95	$94.00
Purchase #7	$209.37	4.678%	$219.1643	$219.16	$219.15	$219.20
7 purchase totals =	$939.90		$1,016.1590	$1,016.15	$1,016.10	$1,016.20