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	$54.56	8.743%	$59.3302	$59.33	$59.35	$59.30
Purchase #2	$119.77	7.132%	$128.312	$128.31	$128.30	$128.30
Purchase #3	$174.37	7.364%	$187.2106	$187.21	$187.20	$187.20
Purchase #4	$49.44	4.412%	$51.6213	$51.62	$51.60	$51.60
Purchase #5	$123.69	10.118%	$136.205	$136.21	$136.20	$136.20
Purchase #6	$49.29	11.270%	$54.845	$54.85	$54.85	$54.80
Purchase #7	$165.78	3.547%	$171.6602	$171.66	$171.65	$171.70
7 purchase totals =	$736.90		$789.1843	$789.19	$789.15	$789.10