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	$193.89	13.618%	$220.2939	$220.29	$220.30	$220.30
Purchase #2	$70.97	10.524%	$78.4389	$78.44	$78.45	$78.40
Purchase #3	$141.78	3.515%	$146.7636	$146.76	$146.75	$146.80
Purchase #4	$39.98	5.512%	$42.1837	$42.18	$42.20	$42.20
Purchase #5	$150.25	5.556%	$158.5979	$158.60	$158.60	$158.60
Purchase #6	$29.36	5.587%	$31.0003	$31.00	$31.00	$31.00
Purchase #7	$157.27	10.626%	$173.9815	$173.98	$174.00	$174.00
7 purchase totals =	$783.50		$851.2598	$851.25	$851.30	$851.30