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	$85.25	6.407%	$90.712	$90.71	$90.70	$90.70
Purchase #2	$159.52	4.129%	$166.1066	$166.11	$166.10	$166.10
Purchase #3	$18.90	7.119%	$20.2455	$20.25	$20.25	$20.20
Purchase #4	$214.55	8.131%	$231.9951	$232.00	$232.00	$232.00
Purchase #5	$109.75	12.393%	$123.3513	$123.35	$123.35	$123.40
Purchase #6	$96.29	4.208%	$100.3419	$100.34	$100.35	$100.30
Purchase #7	$204.59	7.213%	$219.3471	$219.35	$219.35	$219.30
7 purchase totals =	$888.85		$952.0995	$952.11	$952.10	$952.00