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	$24.38	6.201%	$25.8918	$25.89	$25.90	$25.90
Purchase #2	$246.43	12.715%	$277.7636	$277.76	$277.75	$277.80
Purchase #3	$158.65	4.193%	$165.3022	$165.30	$165.30	$165.30
Purchase #4	$208.39	5.329%	$219.4951	$219.50	$219.50	$219.50
Purchase #5	$228.50	6.152%	$242.5573	$242.56	$242.55	$242.60
Purchase #6	$105.72	13.851%	$120.3633	$120.36	$120.35	$120.40
Purchase #7	$82.35	10.272%	$90.809	$90.81	$90.80	$90.80
7 purchase totals =	$1,054.42		$1,142.1823	$1,142.18	$1,142.15	$1,142.30