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	$135.73	4.268%	$141.523	$141.52	$141.50	$141.50
Purchase #2	$96.33	7.357%	$103.417	$103.42	$103.40	$103.40
Purchase #3	$95.95	3.799%	$99.5951	$99.60	$99.60	$99.60
Purchase #4	$186.27	7.548%	$200.3297	$200.33	$200.35	$200.30
Purchase #5	$40.82	4.784%	$42.7728	$42.77	$42.75	$42.80
Purchase #6	$161.76	12.526%	$182.0221	$182.02	$182.00	$182.00
Purchase #7	$39.69	4.477%	$41.4669	$41.47	$41.45	$41.50
7 purchase totals =	$756.55		$811.1266	$811.13	$811.05	$811.10