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	$74.50	11.222%	$82.8604	$82.86	$82.85	$82.90
Purchase #2	$209.45	5.547%	$221.0682	$221.07	$221.05	$221.10
Purchase #3	$150.60	11.421%	$167.8	$167.80	$167.80	$167.80
Purchase #4	$216.83	3.479%	$224.3735	$224.37	$224.35	$224.40
Purchase #5	$94.31	10.772%	$104.4691	$104.47	$104.45	$104.50
Purchase #6	$49.46	6.424%	$52.6373	$52.64	$52.65	$52.60
Purchase #7	$106.91	12.267%	$120.0246	$120.02	$120.00	$120.00
7 purchase totals =	$902.06		$973.2331	$973.23	$973.15	$973.30