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	$160.83	6.691%	$171.5911	$171.59	$171.60	$171.60
Purchase #2	$216.67	5.569%	$228.7364	$228.74	$228.75	$228.70
Purchase #3	$170.48	8.804%	$185.4891	$185.49	$185.50	$185.50
Purchase #4	$38.86	8.278%	$42.0768	$42.08	$42.10	$42.10
Purchase #5	$70.89	9.502%	$77.626	$77.63	$77.65	$77.60
Purchase #6	$152.31	10.480%	$168.2721	$168.27	$168.25	$168.30
Purchase #7	$42.90	4.790%	$44.9549	$44.95	$44.95	$45.00
7 purchase totals =	$852.94		$918.7464	$918.75	$918.80	$918.80