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	$241.25	11.809%	$269.7392	$269.74	$269.75	$269.70
Purchase #2	$107.95	10.249%	$119.0138	$119.01	$119.00	$119.00
Purchase #3	$67.89	7.312%	$72.8541	$72.85	$72.85	$72.90
Purchase #4	$46.90	10.643%	$51.8916	$51.89	$51.90	$51.90
Purchase #5	$169.58	11.404%	$188.9189	$188.92	$188.90	$188.90
Purchase #6	$81.75	9.865%	$89.8146	$89.81	$89.80	$89.80
Purchase #7	$16.47	12.740%	$18.5683	$18.57	$18.55	$18.60
7 purchase totals =	$731.79		$810.8005	$810.79	$810.75	$810.80