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	$50.47	3.608%	$52.291	$52.29	$52.30	$52.30
Purchase #2	$123.65	5.143%	$130.0093	$130.01	$130.00	$130.00
Purchase #3	$162.40	5.819%	$171.8501	$171.85	$171.85	$171.90
Purchase #4	$91.76	11.739%	$102.5317	$102.53	$102.55	$102.50
Purchase #5	$38.88	9.405%	$42.5367	$42.54	$42.55	$42.50
Purchase #6	$231.30	10.493%	$255.5703	$255.57	$255.55	$255.60
Purchase #7	$171.38	7.350%	$183.9764	$183.98	$184.00	$184.00
7 purchase totals =	$869.84		$938.7655	$938.77	$938.80	$938.80