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	$101.76	3.254%	$105.0713	$105.07	$105.05	$105.10
Purchase #2	$110.69	9.818%	$121.5575	$121.56	$121.55	$121.60
Purchase #3	$111.66	9.687%	$122.4765	$122.48	$122.50	$122.50
Purchase #4	$55.60	7.550%	$59.7978	$59.80	$59.80	$59.80
Purchase #5	$45.59	11.620%	$50.8876	$50.89	$50.90	$50.90
Purchase #6	$33.26	13.454%	$37.7348	$37.73	$37.75	$37.70
Purchase #7	$167.45	9.242%	$182.9257	$182.93	$182.95	$182.90
7 purchase totals =	$626.01		$680.4512	$680.46	$680.50	$680.50