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	$52.36	12.863%	$59.0951	$59.10	$59.10	$59.10
Purchase #2	$149.94	10.627%	$165.8741	$165.87	$165.85	$165.90
Purchase #3	$91.91	4.492%	$96.0386	$96.04	$96.05	$96.00
Purchase #4	$157.44	3.442%	$162.8591	$162.86	$162.85	$162.90
Purchase #5	$131.28	11.560%	$146.456	$146.46	$146.45	$146.50
Purchase #6	$38.30	10.811%	$42.4406	$42.44	$42.45	$42.40
Purchase #7	$185.33	8.106%	$200.3528	$200.35	$200.35	$200.40
7 purchase totals =	$806.56		$873.1163	$873.12	$873.10	$873.20