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	$37.51	13.719%	$42.656	$42.66	$42.65	$42.70
Purchase #2	$114.63	7.766%	$123.5322	$123.53	$123.55	$123.50
Purchase #3	$218.84	13.563%	$248.5213	$248.52	$248.50	$248.50
Purchase #4	$206.96	6.740%	$220.9091	$220.91	$220.90	$220.90
Purchase #5	$75.71	9.108%	$82.6057	$82.61	$82.60	$82.60
Purchase #6	$195.54	12.334%	$219.6579	$219.66	$219.65	$219.70
Purchase #7	$120.81	13.865%	$137.5603	$137.56	$137.55	$137.60
7 purchase totals =	$970.00		$1,075.4425	$1,075.45	$1,075.40	$1,075.50