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	$89.73	12.358%	$100.8188	$100.82	$100.80	$100.80
Purchase #2	$228.40	6.376%	$242.9628	$242.96	$242.95	$243.00
Purchase #3	$42.39	4.121%	$44.1369	$44.14	$44.15	$44.10
Purchase #4	$88.72	12.270%	$99.6059	$99.61	$99.60	$99.60
Purchase #5	$226.71	10.583%	$250.7027	$250.70	$250.70	$250.70
Purchase #6	$227.48	9.294%	$248.622	$248.62	$248.60	$248.60
Purchase #7	$194.94	9.770%	$213.9856	$213.99	$214.00	$214.00
7 purchase totals =	$1,098.37		$1,200.8347	$1,200.84	$1,200.80	$1,200.80