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	$27.97	8.670%	$30.395	$30.40	$30.40	$30.40
Purchase #2	$148.27	11.660%	$165.5583	$165.56	$165.55	$165.60
Purchase #3	$180.66	6.565%	$192.5203	$192.52	$192.50	$192.50
Purchase #4	$64.88	3.145%	$66.9205	$66.92	$66.90	$66.90
Purchase #5	$145.29	4.538%	$151.8833	$151.88	$151.90	$151.90
Purchase #6	$165.78	5.165%	$174.3425	$174.34	$174.35	$174.30
Purchase #7	$89.94	9.304%	$98.308	$98.31	$98.30	$98.30
7 purchase totals =	$822.79		$879.9279	$879.93	$879.90	$879.90