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	$113.72	5.794%	$120.3089	$120.31	$120.30	$120.30
Purchase #2	$215.72	6.425%	$229.58	$229.58	$229.60	$229.60
Purchase #3	$135.46	6.748%	$144.6008	$144.60	$144.60	$144.60
Purchase #4	$86.58	3.557%	$89.6597	$89.66	$89.65	$89.70
Purchase #5	$188.36	6.229%	$200.0929	$200.09	$200.10	$200.10
Purchase #6	$196.43	13.321%	$222.5964	$222.60	$222.60	$222.60
Purchase #7	$164.73	10.395%	$181.8537	$181.85	$181.85	$181.90
7 purchase totals =	$1,101.00		$1,188.6924	$1,188.69	$1,188.70	$1,188.80