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	$92.41	10.705%	$102.3025	$102.30	$102.30	$102.30
Purchase #2	$111.46	4.121%	$116.0533	$116.05	$116.05	$116.10
Purchase #3	$111.92	8.529%	$121.4657	$121.47	$121.45	$121.50
Purchase #4	$91.41	12.151%	$102.5172	$102.52	$102.50	$102.50
Purchase #5	$81.40	9.331%	$88.9954	$89.00	$89.00	$89.00
Purchase #6	$156.75	3.296%	$161.9165	$161.92	$161.90	$161.90
Purchase #7	$64.69	10.294%	$71.3492	$71.35	$71.35	$71.30
7 purchase totals =	$710.04		$764.5998	$764.61	$764.55	$764.60