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	$223.90	3.446%	$231.6156	$231.62	$231.60	$231.60
Purchase #2	$103.39	8.226%	$111.8949	$111.89	$111.90	$111.90
Purchase #3	$26.28	5.318%	$27.6776	$27.68	$27.70	$27.70
Purchase #4	$98.86	11.791%	$110.5166	$110.52	$110.50	$110.50
Purchase #5	$142.89	12.804%	$161.1856	$161.19	$161.20	$161.20
Purchase #6	$249.69	7.524%	$268.4767	$268.48	$268.50	$268.50
Purchase #7	$126.87	11.565%	$141.5425	$141.54	$141.55	$141.50
7 purchase totals =	$971.88		$1,052.9095	$1,052.92	$1,052.95	$1,052.90