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	$163.71	4.798%	$171.5648	$171.56	$171.55	$171.60
Purchase #2	$55.82	7.626%	$60.0768	$60.08	$60.10	$60.10
Purchase #3	$218.27	11.139%	$242.5831	$242.58	$242.60	$242.60
Purchase #4	$211.28	3.488%	$218.6494	$218.65	$218.65	$218.60
Purchase #5	$110.87	11.394%	$123.5025	$123.50	$123.50	$123.50
Purchase #6	$66.90	8.223%	$72.4012	$72.40	$72.40	$72.40
Purchase #7	$80.34	3.414%	$83.0828	$83.08	$83.10	$83.10
7 purchase totals =	$907.19		$971.8606	$971.85	$971.90	$971.90