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	$41.81	9.645%	$45.8426	$45.84	$45.85	$45.80
Purchase #2	$54.98	7.830%	$59.2849	$59.28	$59.30	$59.30
Purchase #3	$175.78	13.381%	$199.3011	$199.30	$199.30	$199.30
Purchase #4	$73.34	10.269%	$80.8713	$80.87	$80.85	$80.90
Purchase #5	$117.77	7.805%	$126.9619	$126.96	$126.95	$127.00
Purchase #6	$23.96	4.605%	$25.0634	$25.06	$25.05	$25.10
Purchase #7	$159.82	9.663%	$175.2634	$175.26	$175.25	$175.30
7 purchase totals =	$647.46		$712.5886	$712.57	$712.55	$712.70