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	$127.85	5.562%	$134.961	$134.96	$134.95	$135.00
Purchase #2	$20.44	7.108%	$21.8929	$21.89	$21.90	$21.90
Purchase #3	$243.69	12.366%	$273.8247	$273.82	$273.80	$273.80
Purchase #4	$33.28	12.392%	$37.4041	$37.40	$37.40	$37.40
Purchase #5	$72.44	10.589%	$80.1107	$80.11	$80.10	$80.10
Purchase #6	$24.78	4.577%	$25.9142	$25.91	$25.90	$25.90
Purchase #7	$67.81	4.798%	$71.0635	$71.06	$71.05	$71.10
7 purchase totals =	$590.29		$645.1711	$645.15	$645.10	$645.20