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	$54.49	8.789%	$59.2791	$59.28	$59.30	$59.30
Purchase #2	$71.64	9.735%	$78.6142	$78.61	$78.60	$78.60
Purchase #3	$196.86	11.569%	$219.6347	$219.63	$219.65	$219.60
Purchase #4	$27.96	4.770%	$29.2937	$29.29	$29.30	$29.30
Purchase #5	$101.30	4.544%	$105.9031	$105.90	$105.90	$105.90
Purchase #6	$144.47	11.825%	$161.5536	$161.55	$161.55	$161.60
Purchase #7	$226.49	6.192%	$240.5143	$240.51	$240.50	$240.50
7 purchase totals =	$823.21		$894.7927	$894.77	$894.80	$894.80