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	$37.47	5.117%	$39.3873	$39.39	$39.40	$39.40
Purchase #2	$30.80	9.789%	$33.815	$33.82	$33.80	$33.80
Purchase #3	$242.37	4.642%	$253.6208	$253.62	$253.60	$253.60
Purchase #4	$76.79	8.237%	$83.1152	$83.12	$83.10	$83.10
Purchase #5	$177.55	4.460%	$185.4687	$185.47	$185.45	$185.50
Purchase #6	$207.45	3.692%	$215.1091	$215.11	$215.10	$215.10
Purchase #7	$206.62	11.222%	$229.8069	$229.81	$229.80	$229.80
7 purchase totals =	$979.05		$1,040.3230	$1,040.34	$1,040.25	$1,040.30