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	$85.78	6.446%	$91.3094	$91.31	$91.30	$91.30
Purchase #2	$200.66	10.709%	$222.1487	$222.15	$222.15	$222.10
Purchase #3	$181.51	8.489%	$196.9184	$196.92	$196.90	$196.90
Purchase #4	$236.66	4.391%	$247.0517	$247.05	$247.05	$247.10
Purchase #5	$173.88	8.453%	$188.5781	$188.58	$188.60	$188.60
Purchase #6	$247.63	5.752%	$261.8737	$261.87	$261.85	$261.90
Purchase #7	$172.76	9.590%	$189.3277	$189.33	$189.35	$189.30
7 purchase totals =	$1,298.88		$1,397.2077	$1,397.21	$1,397.20	$1,397.20