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	$238.97	6.631%	$254.8161	$254.82	$254.80	$254.80
Purchase #2	$144.58	3.470%	$149.5969	$149.60	$149.60	$149.60
Purchase #3	$159.94	11.837%	$178.8721	$178.87	$178.85	$178.90
Purchase #4	$82.27	5.578%	$86.859	$86.86	$86.85	$86.90
Purchase #5	$67.58	7.401%	$72.5816	$72.58	$72.60	$72.60
Purchase #6	$26.75	6.313%	$28.4387	$28.44	$28.45	$28.40
Purchase #7	$51.91	7.766%	$55.9413	$55.94	$55.95	$55.90
7 purchase totals =	$772.00		$827.1057	$827.11	$827.10	$827.10