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	$49.32	11.558%	$55.0204	$55.02	$55.00	$55.00
Purchase #2	$39.54	6.750%	$42.209	$42.21	$42.20	$42.20
Purchase #3	$50.38	7.120%	$53.9671	$53.97	$53.95	$54.00
Purchase #4	$195.77	6.138%	$207.7864	$207.79	$207.80	$207.80
Purchase #5	$123.56	13.784%	$140.5915	$140.59	$140.60	$140.60
Purchase #6	$99.33	6.484%	$105.7706	$105.77	$105.75	$105.80
Purchase #7	$124.76	13.453%	$141.544	$141.54	$141.55	$141.50
7 purchase totals =	$682.66		$746.8890	$746.89	$746.85	$746.90