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	$35.35	5.206%	$37.1903	$37.19	$37.20	$37.20
Purchase #2	$165.89	10.846%	$183.8824	$183.88	$183.90	$183.90
Purchase #3	$146.91	12.745%	$165.6337	$165.63	$165.65	$165.60
Purchase #4	$60.88	4.583%	$63.6701	$63.67	$63.65	$63.70
Purchase #5	$35.89	3.838%	$37.2675	$37.27	$37.25	$37.30
Purchase #6	$79.27	9.303%	$86.6445	$86.64	$86.65	$86.60
Purchase #7	$95.54	6.500%	$101.7501	$101.75	$101.75	$101.80
7 purchase totals =	$619.73		$676.0386	$676.03	$676.05	$676.10