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	$18.68	9.269%	$20.4114	$20.41	$20.40	$20.40
Purchase #2	$34.89	11.786%	$39.0021	$39.00	$39.00	$39.00
Purchase #3	$30.96	8.430%	$33.5699	$33.57	$33.55	$33.60
Purchase #4	$176.40	6.768%	$188.3388	$188.34	$188.35	$188.30
Purchase #5	$217.46	6.568%	$231.7428	$231.74	$231.75	$231.70
Purchase #6	$56.25	6.221%	$59.7493	$59.75	$59.75	$59.70
Purchase #7	$233.39	12.582%	$262.7551	$262.76	$262.75	$262.80
7 purchase totals =	$768.03		$835.5694	$835.57	$835.55	$835.50