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	$49.63	12.273%	$55.7211	$55.72	$55.70	$55.70
Purchase #2	$98.58	6.106%	$104.5993	$104.60	$104.60	$104.60
Purchase #3	$56.84	4.162%	$59.2057	$59.21	$59.20	$59.20
Purchase #4	$211.60	5.794%	$223.8601	$223.86	$223.85	$223.90
Purchase #5	$13.91	9.131%	$15.1801	$15.18	$15.20	$15.20
Purchase #6	$39.72	6.776%	$42.4114	$42.41	$42.40	$42.40
Purchase #7	$249.49	7.319%	$267.7502	$267.75	$267.75	$267.80
7 purchase totals =	$719.77		$768.7279	$768.73	$768.70	$768.80