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	$94.94	5.481%	$100.1437	$100.14	$100.15	$100.10
Purchase #2	$245.65	10.852%	$272.3079	$272.31	$272.30	$272.30
Purchase #3	$201.91	11.107%	$224.3361	$224.34	$224.35	$224.30
Purchase #4	$91.81	6.754%	$98.0108	$98.01	$98.00	$98.00
Purchase #5	$47.72	11.322%	$53.1229	$53.12	$53.10	$53.10
Purchase #6	$92.94	6.184%	$98.6874	$98.69	$98.70	$98.70
Purchase #7	$110.46	11.664%	$123.3441	$123.34	$123.35	$123.30
7 purchase totals =	$885.43		$969.9529	$969.95	$969.95	$969.80