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	$96.25	13.328%	$109.0782	$109.08	$109.10	$109.10
Purchase #2	$81.31	8.528%	$88.2441	$88.24	$88.25	$88.20
Purchase #3	$230.65	12.329%	$259.0868	$259.09	$259.10	$259.10
Purchase #4	$110.84	11.470%	$123.5533	$123.55	$123.55	$123.60
Purchase #5	$37.70	4.416%	$39.3648	$39.36	$39.35	$39.40
Purchase #6	$30.46	8.570%	$33.0704	$33.07	$33.05	$33.10
Purchase #7	$76.33	5.223%	$80.3167	$80.32	$80.30	$80.30
7 purchase totals =	$663.54		$732.7143	$732.71	$732.70	$732.80