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	$171.38	3.785%	$177.8667	$177.87	$177.85	$177.90
Purchase #2	$127.70	3.591%	$132.2857	$132.29	$132.30	$132.30
Purchase #3	$38.31	5.766%	$40.519	$40.52	$40.50	$40.50
Purchase #4	$136.31	12.127%	$152.8403	$152.84	$152.85	$152.80
Purchase #5	$39.55	6.541%	$42.137	$42.14	$42.15	$42.10
Purchase #6	$37.75	11.593%	$42.1264	$42.13	$42.15	$42.10
Purchase #7	$250.26	7.301%	$268.5315	$268.53	$268.55	$268.50
7 purchase totals =	$801.26		$856.3066	$856.32	$856.35	$856.20