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	$59.79	7.851%	$64.4841	$64.48	$64.50	$64.50
Purchase #2	$247.47	12.729%	$278.9705	$278.97	$278.95	$279.00
Purchase #3	$68.56	4.842%	$71.8797	$71.88	$71.90	$71.90
Purchase #4	$36.26	9.852%	$39.8323	$39.83	$39.85	$39.80
Purchase #5	$30.91	4.686%	$32.3584	$32.36	$32.35	$32.40
Purchase #6	$246.35	7.352%	$264.4617	$264.46	$264.45	$264.50
Purchase #7	$131.68	10.862%	$145.9831	$145.98	$146.00	$146.00
7 purchase totals =	$821.02		$897.9698	$897.96	$898.00	$898.10