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	$35.27	13.736%	$40.1147	$40.11	$40.10	$40.10
Purchase #2	$250.77	13.608%	$284.8948	$284.89	$284.90	$284.90
Purchase #3	$179.61	11.684%	$200.5956	$200.60	$200.60	$200.60
Purchase #4	$214.47	4.701%	$224.5522	$224.55	$224.55	$224.60
Purchase #5	$23.68	7.281%	$25.4041	$25.40	$25.40	$25.40
Purchase #6	$134.74	4.804%	$141.2129	$141.21	$141.20	$141.20
Purchase #7	$206.59	9.191%	$225.5777	$225.58	$225.60	$225.60
7 purchase totals =	$1,045.13		$1,142.3520	$1,142.34	$1,142.35	$1,142.40