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	$72.41	7.421%	$77.7835	$77.78	$77.80	$77.80
Purchase #2	$45.37	10.573%	$50.167	$50.17	$50.15	$50.20
Purchase #3	$149.40	10.737%	$165.4411	$165.44	$165.45	$165.40
Purchase #4	$174.82	12.314%	$196.3473	$196.35	$196.35	$196.30
Purchase #5	$152.52	3.241%	$157.4632	$157.46	$157.45	$157.50
Purchase #6	$100.78	5.451%	$106.2735	$106.27	$106.25	$106.30
Purchase #7	$154.97	6.244%	$164.6463	$164.65	$164.65	$164.60
7 purchase totals =	$850.27		$918.1219	$918.12	$918.10	$918.10