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	$43.44	9.308%	$47.4834	$47.48	$47.50	$47.50
Purchase #2	$81.74	5.257%	$86.0371	$86.04	$86.05	$86.00
Purchase #3	$206.56	11.182%	$229.6575	$229.66	$229.65	$229.70
Purchase #4	$14.65	5.498%	$15.4555	$15.46	$15.45	$15.50
Purchase #5	$76.76	9.285%	$83.8872	$83.89	$83.90	$83.90
Purchase #6	$172.52	5.638%	$182.2467	$182.25	$182.25	$182.20
Purchase #7	$30.48	9.166%	$33.2738	$33.27	$33.25	$33.30
7 purchase totals =	$626.15		$678.0412	$678.05	$678.05	$678.10