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	$112.45	6.139%	$119.3533	$119.35	$119.35	$119.40
Purchase #2	$250.77	8.300%	$271.5839	$271.58	$271.60	$271.60
Purchase #3	$209.95	3.510%	$217.3192	$217.32	$217.30	$217.30
Purchase #4	$36.41	10.640%	$40.284	$40.28	$40.30	$40.30
Purchase #5	$71.58	8.285%	$77.5104	$77.51	$77.50	$77.50
Purchase #6	$52.92	13.223%	$59.9176	$59.92	$59.90	$59.90
Purchase #7	$137.59	8.539%	$149.3388	$149.34	$149.35	$149.30
7 purchase totals =	$871.67		$935.3072	$935.30	$935.30	$935.30