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	$29.34	8.701%	$31.8929	$31.89	$31.90	$31.90
Purchase #2	$16.82	4.340%	$17.55	$17.55	$17.55	$17.60
Purchase #3	$42.91	12.166%	$48.1304	$48.13	$48.15	$48.10
Purchase #4	$187.73	5.525%	$198.1021	$198.10	$198.10	$198.10
Purchase #5	$149.80	10.557%	$165.6144	$165.61	$165.60	$165.60
Purchase #6	$23.96	13.736%	$27.2511	$27.25	$27.25	$27.30
Purchase #7	$40.86	3.599%	$42.3306	$42.33	$42.35	$42.30
7 purchase totals =	$491.42		$530.8715	$530.86	$530.90	$530.90