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	$123.50	8.419%	$133.8975	$133.90	$133.90	$133.90
Purchase #2	$98.32	11.840%	$109.9611	$109.96	$109.95	$110.00
Purchase #3	$179.53	3.386%	$185.6089	$185.61	$185.60	$185.60
Purchase #4	$102.88	9.603%	$112.7596	$112.76	$112.75	$112.80
Purchase #5	$172.42	5.111%	$181.2324	$181.23	$181.25	$181.20
Purchase #6	$64.63	12.507%	$72.7133	$72.71	$72.70	$72.70
Purchase #7	$22.48	11.212%	$25.0005	$25.00	$25.00	$25.00
7 purchase totals =	$763.76		$821.1733	$821.17	$821.15	$821.20