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	$201.60	11.798%	$225.3848	$225.38	$225.40	$225.40
Purchase #2	$231.33	4.629%	$242.0383	$242.04	$242.05	$242.00
Purchase #3	$36.57	3.662%	$37.9092	$37.91	$37.90	$37.90
Purchase #4	$193.35	9.706%	$212.1166	$212.12	$212.10	$212.10
Purchase #5	$29.50	9.484%	$32.2978	$32.30	$32.30	$32.30
Purchase #6	$139.77	9.142%	$152.5478	$152.55	$152.55	$152.50
Purchase #7	$29.58	12.744%	$33.3497	$33.35	$33.35	$33.30
7 purchase totals =	$861.70		$935.6442	$935.65	$935.65	$935.50