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	$229.89	10.111%	$253.1342	$253.13	$253.15	$253.10
Purchase #2	$112.95	10.135%	$124.3975	$124.40	$124.40	$124.40
Purchase #3	$65.41	9.175%	$71.4114	$71.41	$71.40	$71.40
Purchase #4	$96.46	8.594%	$104.7498	$104.75	$104.75	$104.70
Purchase #5	$16.43	12.401%	$18.4675	$18.47	$18.45	$18.50
Purchase #6	$171.65	5.355%	$180.8419	$180.84	$180.85	$180.80
Purchase #7	$81.34	10.490%	$89.8726	$89.87	$89.85	$89.90
7 purchase totals =	$774.13		$842.8749	$842.87	$842.85	$842.80