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	$45.43	4.278%	$47.3735	$47.37	$47.35	$47.40
Purchase #2	$25.53	8.230%	$27.6311	$27.63	$27.65	$27.60
Purchase #3	$174.78	9.802%	$191.9119	$191.91	$191.90	$191.90
Purchase #4	$122.53	12.548%	$137.9051	$137.91	$137.90	$137.90
Purchase #5	$36.71	10.107%	$40.4203	$40.42	$40.40	$40.40
Purchase #6	$232.92	4.822%	$244.1514	$244.15	$244.15	$244.20
Purchase #7	$92.26	12.308%	$103.6154	$103.62	$103.60	$103.60
7 purchase totals =	$730.16		$793.0087	$793.01	$792.95	$793.00