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	$51.61	11.758%	$57.6783	$57.68	$57.70	$57.70
Purchase #2	$182.30	3.181%	$188.099	$188.10	$188.10	$188.10
Purchase #3	$90.48	4.812%	$94.8339	$94.83	$94.85	$94.80
Purchase #4	$104.54	7.338%	$112.2111	$112.21	$112.20	$112.20
Purchase #5	$173.64	3.584%	$179.8633	$179.86	$179.85	$179.90
Purchase #6	$37.73	11.561%	$42.092	$42.09	$42.10	$42.10
Purchase #7	$214.29	3.328%	$221.4216	$221.42	$221.40	$221.40
7 purchase totals =	$854.59		$896.1992	$896.19	$896.20	$896.20