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	$131.35	11.755%	$146.7902	$146.79	$146.80	$146.80
Purchase #2	$167.97	3.497%	$173.8439	$173.84	$173.85	$173.80
Purchase #3	$123.30	10.206%	$135.884	$135.88	$135.90	$135.90
Purchase #4	$79.39	12.622%	$89.4106	$89.41	$89.40	$89.40
Purchase #5	$92.95	13.649%	$105.6367	$105.64	$105.65	$105.60
Purchase #6	$94.89	13.333%	$107.5417	$107.54	$107.55	$107.50
Purchase #7	$23.60	8.549%	$25.6176	$25.62	$25.60	$25.60
7 purchase totals =	$713.45		$784.7247	$784.72	$784.75	$784.60