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	$81.68	9.592%	$89.5147	$89.51	$89.50	$89.50
Purchase #2	$6.48	6.534%	$6.9034	$6.90	$6.90	$6.90
Purchase #3	$112.64	4.667%	$117.8969	$117.90	$117.90	$117.90
Purchase #4	$17.57	7.463%	$18.8812	$18.88	$18.90	$18.90
Purchase #5	$76.38	7.862%	$82.385	$82.39	$82.40	$82.40
Purchase #6	$170.90	7.835%	$184.29	$184.29	$184.30	$184.30
Purchase #7	$99.66	9.281%	$108.9094	$108.91	$108.90	$108.90
7 purchase totals =	$565.31		$608.7806	$608.78	$608.80	$608.80