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	$171.37	4.340%	$178.8075	$178.81	$178.80	$178.80
Purchase #2	$128.54	10.709%	$142.3053	$142.31	$142.30	$142.30
Purchase #3	$119.75	6.418%	$127.4356	$127.44	$127.45	$127.40
Purchase #4	$106.26	9.685%	$116.5513	$116.55	$116.55	$116.60
Purchase #5	$80.31	6.535%	$85.5583	$85.56	$85.55	$85.60
Purchase #6	$233.48	7.782%	$251.6494	$251.65	$251.65	$251.60
Purchase #7	$36.36	6.685%	$38.7907	$38.79	$38.80	$38.80
7 purchase totals =	$876.07		$941.0981	$941.11	$941.10	$941.10