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	$93.76	6.268%	$99.6369	$99.64	$99.65	$99.60
Purchase #2	$157.51	7.709%	$169.6524	$169.65	$169.65	$169.70
Purchase #3	$96.87	8.839%	$105.4323	$105.43	$105.45	$105.40
Purchase #4	$162.45	8.115%	$175.6328	$175.63	$175.65	$175.60
Purchase #5	$179.76	9.179%	$196.2602	$196.26	$196.25	$196.30
Purchase #6	$46.43	9.159%	$50.6825	$50.68	$50.70	$50.70
Purchase #7	$115.96	9.849%	$127.3809	$127.38	$127.40	$127.40
7 purchase totals =	$852.74		$924.6780	$924.67	$924.75	$924.70