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	$71.47	11.184%	$79.4632	$79.46	$79.45	$79.50
Purchase #2	$232.48	9.410%	$254.3564	$254.36	$254.35	$254.40
Purchase #3	$125.48	13.820%	$142.8213	$142.82	$142.80	$142.80
Purchase #4	$245.40	13.496%	$278.5192	$278.52	$278.50	$278.50
Purchase #5	$230.68	10.696%	$255.3535	$255.35	$255.35	$255.40
Purchase #6	$45.45	7.596%	$48.9024	$48.90	$48.90	$48.90
Purchase #7	$63.94	6.570%	$68.1409	$68.14	$68.15	$68.10
7 purchase totals =	$1,014.90		$1,127.5569	$1,127.55	$1,127.50	$1,127.60