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	$29.98	7.153%	$32.1245	$32.12	$32.10	$32.10
Purchase #2	$218.40	7.369%	$234.4939	$234.49	$234.50	$234.50
Purchase #3	$23.60	7.283%	$25.3188	$25.32	$25.30	$25.30
Purchase #4	$211.31	13.779%	$240.4264	$240.43	$240.45	$240.40
Purchase #5	$139.39	9.400%	$152.4927	$152.49	$152.50	$152.50
Purchase #6	$159.88	13.285%	$181.1201	$181.12	$181.10	$181.10
Purchase #7	$106.76	4.511%	$111.5759	$111.58	$111.60	$111.60
7 purchase totals =	$889.32		$977.5523	$977.55	$977.55	$977.50