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	$70.53	9.789%	$77.4342	$77.43	$77.45	$77.40
Purchase #2	$138.30	6.314%	$147.0323	$147.03	$147.05	$147.00
Purchase #3	$22.59	12.577%	$25.4311	$25.43	$25.45	$25.40
Purchase #4	$171.43	13.401%	$194.4033	$194.40	$194.40	$194.40
Purchase #5	$59.41	9.740%	$65.1965	$65.20	$65.20	$65.20
Purchase #6	$18.29	11.865%	$20.4601	$20.46	$20.45	$20.50
Purchase #7	$69.91	5.666%	$73.8711	$73.87	$73.85	$73.90
7 purchase totals =	$550.46		$603.8286	$603.82	$603.85	$603.80