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	$10.87	8.464%	$11.79	$11.79	$11.80	$11.80
Purchase #2	$232.85	5.237%	$245.0444	$245.04	$245.05	$245.00
Purchase #3	$78.65	6.185%	$83.5145	$83.51	$83.50	$83.50
Purchase #4	$158.60	4.851%	$166.2937	$166.29	$166.30	$166.30
Purchase #5	$42.39	12.287%	$47.5985	$47.60	$47.60	$47.60
Purchase #6	$85.89	9.753%	$94.2669	$94.27	$94.25	$94.30
Purchase #7	$43.98	3.119%	$45.3517	$45.35	$45.35	$45.40
7 purchase totals =	$653.23		$693.8597	$693.85	$693.85	$693.90