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	$198.87	12.339%	$223.4086	$223.41	$223.40	$223.40
Purchase #2	$205.98	11.602%	$229.8778	$229.88	$229.90	$229.90
Purchase #3	$99.30	6.689%	$105.9422	$105.94	$105.95	$105.90
Purchase #4	$213.26	8.151%	$230.6428	$230.64	$230.65	$230.60
Purchase #5	$73.77	4.510%	$77.097	$77.10	$77.10	$77.10
Purchase #6	$240.44	10.469%	$265.6117	$265.61	$265.60	$265.60
Purchase #7	$61.37	10.590%	$67.8691	$67.87	$67.85	$67.90
7 purchase totals =	$1,092.99		$1,200.4492	$1,200.45	$1,200.45	$1,200.40