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	$97.28	6.184%	$103.2958	$103.30	$103.30	$103.30
Purchase #2	$19.72	5.661%	$20.8363	$20.84	$20.85	$20.80
Purchase #3	$36.63	10.182%	$40.3597	$40.36	$40.35	$40.40
Purchase #4	$177.58	6.342%	$188.8421	$188.84	$188.85	$188.80
Purchase #5	$210.89	7.691%	$227.1095	$227.11	$227.10	$227.10
Purchase #6	$42.63	6.205%	$45.2752	$45.28	$45.30	$45.30
Purchase #7	$210.85	13.865%	$240.0844	$240.08	$240.10	$240.10
7 purchase totals =	$795.58		$865.8030	$865.81	$865.85	$865.80