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	$39.45	9.755%	$43.2983	$43.30	$43.30	$43.30
Purchase #2	$29.79	9.690%	$32.6767	$32.68	$32.70	$32.70
Purchase #3	$176.57	7.822%	$190.3813	$190.38	$190.40	$190.40
Purchase #4	$216.40	12.521%	$243.4954	$243.50	$243.50	$243.50
Purchase #5	$103.99	4.163%	$108.3191	$108.32	$108.30	$108.30
Purchase #6	$85.64	5.760%	$90.5729	$90.57	$90.55	$90.60
Purchase #7	$91.45	4.206%	$95.2964	$95.30	$95.30	$95.30
7 purchase totals =	$743.29		$804.0401	$804.05	$804.05	$804.10