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	$30.46	10.221%	$33.5733	$33.57	$33.55	$33.60
Purchase #2	$131.42	5.129%	$138.1605	$138.16	$138.15	$138.20
Purchase #3	$48.35	12.125%	$54.2124	$54.21	$54.20	$54.20
Purchase #4	$206.73	10.559%	$228.5586	$228.56	$228.55	$228.60
Purchase #5	$87.36	12.341%	$98.1411	$98.14	$98.15	$98.10
Purchase #6	$65.56	10.263%	$72.2884	$72.29	$72.30	$72.30
Purchase #7	$99.28	6.674%	$105.9059	$105.91	$105.90	$105.90
7 purchase totals =	$669.16		$730.8402	$730.84	$730.80	$730.90