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	$232.48	9.810%	$255.2863	$255.29	$255.30	$255.30
Purchase #2	$164.62	4.569%	$172.1415	$172.14	$172.15	$172.10
Purchase #3	$39.68	7.515%	$42.662	$42.66	$42.65	$42.70
Purchase #4	$125.47	12.667%	$141.3633	$141.36	$141.35	$141.40
Purchase #5	$55.83	10.394%	$61.633	$61.63	$61.65	$61.60
Purchase #6	$33.71	9.140%	$36.7911	$36.79	$36.80	$36.80
Purchase #7	$108.61	13.711%	$123.5015	$123.50	$123.50	$123.50
7 purchase totals =	$760.40		$833.3787	$833.37	$833.40	$833.40