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	$82.31	12.734%	$92.7914	$92.79	$92.80	$92.80
Purchase #2	$44.59	4.496%	$46.5948	$46.59	$46.60	$46.60
Purchase #3	$199.36	13.408%	$226.0902	$226.09	$226.10	$226.10
Purchase #4	$98.48	9.217%	$107.5569	$107.56	$107.55	$107.60
Purchase #5	$53.49	11.526%	$59.6553	$59.66	$59.65	$59.70
Purchase #6	$42.49	9.600%	$46.569	$46.57	$46.55	$46.60
Purchase #7	$64.84	9.688%	$71.1217	$71.12	$71.10	$71.10
7 purchase totals =	$585.56		$650.3793	$650.38	$650.35	$650.50