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	$123.32	6.597%	$131.4554	$131.46	$131.45	$131.50
Purchase #2	$29.85	4.237%	$31.1147	$31.11	$31.10	$31.10
Purchase #3	$181.56	9.670%	$199.1169	$199.12	$199.10	$199.10
Purchase #4	$183.63	13.723%	$208.8295	$208.83	$208.85	$208.80
Purchase #5	$195.50	7.293%	$209.7578	$209.76	$209.75	$209.80
Purchase #6	$83.32	12.145%	$93.4392	$93.44	$93.45	$93.40
Purchase #7	$137.87	13.810%	$156.9098	$156.91	$156.90	$156.90
7 purchase totals =	$935.05		$1,030.6233	$1,030.63	$1,030.60	$1,030.60