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	$81.83	9.445%	$89.5588	$89.56	$89.55	$89.60
Purchase #2	$47.47	10.623%	$52.5127	$52.51	$52.50	$52.50
Purchase #3	$25.60	3.315%	$26.4486	$26.45	$26.45	$26.40
Purchase #4	$211.63	10.697%	$234.2681	$234.27	$234.25	$234.30
Purchase #5	$67.51	12.729%	$76.1033	$76.10	$76.10	$76.10
Purchase #6	$171.92	7.368%	$184.5871	$184.59	$184.60	$184.60
Purchase #7	$71.80	8.506%	$77.9073	$77.91	$77.90	$77.90
7 purchase totals =	$677.76		$741.3859	$741.39	$741.35	$741.40