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	$18.62	10.268%	$20.5319	$20.53	$20.55	$20.50
Purchase #2	$150.45	7.855%	$162.2678	$162.27	$162.25	$162.30
Purchase #3	$35.53	5.298%	$37.4124	$37.41	$37.40	$37.40
Purchase #4	$81.53	4.501%	$85.1997	$85.20	$85.20	$85.20
Purchase #5	$70.36	4.475%	$73.5086	$73.51	$73.50	$73.50
Purchase #6	$133.61	8.843%	$145.4251	$145.43	$145.45	$145.40
Purchase #7	$107.63	6.348%	$114.4624	$114.46	$114.45	$114.50
7 purchase totals =	$597.73		$638.8079	$638.81	$638.80	$638.80