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	$80.65	3.315%	$83.3235	$83.32	$83.30	$83.30
Purchase #2	$20.36	6.518%	$21.6871	$21.69	$21.70	$21.70
Purchase #3	$145.32	12.280%	$163.1653	$163.17	$163.15	$163.20
Purchase #4	$83.89	6.861%	$89.6457	$89.65	$89.65	$89.60
Purchase #5	$241.65	9.761%	$265.2375	$265.24	$265.25	$265.20
Purchase #6	$209.50	6.415%	$222.9394	$222.94	$222.95	$222.90
Purchase #7	$18.39	9.561%	$20.1483	$20.15	$20.15	$20.10
7 purchase totals =	$799.76		$866.1468	$866.16	$866.15	$866.00