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	$139.63	10.407%	$154.1613	$154.16	$154.15	$154.20
Purchase #2	$198.40	11.145%	$220.5117	$220.51	$220.50	$220.50
Purchase #3	$147.25	4.401%	$153.7305	$153.73	$153.75	$153.70
Purchase #4	$124.41	13.197%	$140.8284	$140.83	$140.85	$140.80
Purchase #5	$82.43	5.173%	$86.6941	$86.69	$86.70	$86.70
Purchase #6	$41.27	10.813%	$45.7325	$45.73	$45.75	$45.70
Purchase #7	$246.61	11.199%	$274.2279	$274.23	$274.25	$274.20
7 purchase totals =	$980.00		$1,075.8864	$1,075.88	$1,075.95	$1,075.80