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	$171.72	4.447%	$179.3564	$179.36	$179.35	$179.40
Purchase #2	$141.53	6.215%	$150.3261	$150.33	$150.35	$150.30
Purchase #3	$37.87	12.750%	$42.6984	$42.70	$42.70	$42.70
Purchase #4	$79.40	7.817%	$85.6067	$85.61	$85.60	$85.60
Purchase #5	$74.57	5.584%	$78.734	$78.73	$78.75	$78.70
Purchase #6	$211.62	10.413%	$233.656	$233.66	$233.65	$233.70
Purchase #7	$75.33	4.861%	$78.9918	$78.99	$79.00	$79.00
7 purchase totals =	$792.04		$849.3694	$849.38	$849.40	$849.40