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	$47.78	3.602%	$49.501	$49.50	$49.50	$49.50
Purchase #2	$165.73	3.124%	$170.9074	$170.91	$170.90	$170.90
Purchase #3	$23.89	6.242%	$25.3812	$25.38	$25.40	$25.40
Purchase #4	$82.70	7.822%	$89.1688	$89.17	$89.15	$89.20
Purchase #5	$175.69	5.172%	$184.7767	$184.78	$184.80	$184.80
Purchase #6	$79.94	11.481%	$89.1179	$89.12	$89.10	$89.10
Purchase #7	$12.83	11.716%	$14.3332	$14.33	$14.35	$14.30
7 purchase totals =	$588.56		$623.1862	$623.19	$623.20	$623.20