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	$186.82	6.750%	$199.4304	$199.43	$199.45	$199.40
Purchase #2	$229.42	3.224%	$236.8165	$236.82	$236.80	$236.80
Purchase #3	$28.81	3.662%	$29.865	$29.87	$29.85	$29.90
Purchase #4	$32.82	3.122%	$33.8446	$33.84	$33.85	$33.80
Purchase #5	$77.27	8.514%	$83.8488	$83.85	$83.85	$83.80
Purchase #6	$135.81	5.123%	$142.7675	$142.77	$142.75	$142.80
Purchase #7	$98.98	6.108%	$105.0257	$105.03	$105.05	$105.00
7 purchase totals =	$789.93		$831.5985	$831.61	$831.60	$831.50