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	$35.56	7.622%	$38.2704	$38.27	$38.25	$38.30
Purchase #2	$101.75	7.532%	$109.4138	$109.41	$109.40	$109.40
Purchase #3	$154.61	12.450%	$173.8589	$173.86	$173.85	$173.90
Purchase #4	$190.34	5.152%	$200.1463	$200.15	$200.15	$200.10
Purchase #5	$87.28	3.807%	$90.6027	$90.60	$90.60	$90.60
Purchase #6	$34.40	12.524%	$38.7083	$38.71	$38.70	$38.70
Purchase #7	$8.76	12.410%	$9.8471	$9.85	$9.85	$9.80
7 purchase totals =	$612.70		$660.8475	$660.85	$660.80	$660.80