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	$17.35	4.285%	$18.0934	$18.09	$18.10	$18.10
Purchase #2	$83.72	7.222%	$89.7663	$89.77	$89.75	$89.80
Purchase #3	$181.48	4.816%	$190.2201	$190.22	$190.20	$190.20
Purchase #4	$84.67	7.225%	$90.7874	$90.79	$90.80	$90.80
Purchase #5	$106.36	9.539%	$116.5057	$116.51	$116.50	$116.50
Purchase #6	$55.25	7.389%	$59.3324	$59.33	$59.35	$59.30
Purchase #7	$206.80	10.405%	$228.3175	$228.32	$228.30	$228.30
7 purchase totals =	$735.63		$793.0228	$793.03	$793.00	$793.00