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	$113.56	12.175%	$127.3859	$127.39	$127.40	$127.40
Purchase #2	$32.82	11.382%	$36.5556	$36.56	$36.55	$36.60
Purchase #3	$95.33	8.864%	$103.7801	$103.78	$103.80	$103.80
Purchase #4	$11.94	13.304%	$13.5285	$13.53	$13.55	$13.50
Purchase #5	$165.73	13.701%	$188.4367	$188.44	$188.45	$188.40
Purchase #6	$71.33	9.289%	$77.9558	$77.96	$77.95	$78.00
Purchase #7	$212.78	9.392%	$232.7643	$232.76	$232.75	$232.80
7 purchase totals =	$703.49		$780.4069	$780.42	$780.45	$780.50