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	$84.36	4.720%	$88.3418	$88.34	$88.35	$88.30
Purchase #2	$148.47	10.820%	$164.5345	$164.53	$164.55	$164.50
Purchase #3	$179.90	9.494%	$196.9797	$196.98	$197.00	$197.00
Purchase #4	$124.48	12.421%	$139.9417	$139.94	$139.95	$139.90
Purchase #5	$176.51	6.151%	$187.3671	$187.37	$187.35	$187.40
Purchase #6	$74.28	4.117%	$77.3381	$77.34	$77.35	$77.30
Purchase #7	$133.73	10.853%	$148.2437	$148.24	$148.25	$148.20
7 purchase totals =	$921.73		$1,002.7466	$1,002.74	$1,002.80	$1,002.60