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	$28.51	11.660%	$31.8343	$31.83	$31.85	$31.80
Purchase #2	$30.28	9.755%	$33.2338	$33.23	$33.25	$33.20
Purchase #3	$33.36	11.865%	$37.3182	$37.32	$37.30	$37.30
Purchase #4	$216.49	9.325%	$236.6777	$236.68	$236.70	$236.70
Purchase #5	$242.65	4.612%	$253.841	$253.84	$253.85	$253.80
Purchase #6	$131.93	12.627%	$148.5888	$148.59	$148.60	$148.60
Purchase #7	$104.82	7.673%	$112.8628	$112.86	$112.85	$112.90
7 purchase totals =	$788.04		$854.3566	$854.35	$854.40	$854.30