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	$238.41	13.706%	$271.0865	$271.09	$271.10	$271.10
Purchase #2	$44.74	11.808%	$50.0229	$50.02	$50.00	$50.00
Purchase #3	$51.30	11.750%	$57.3278	$57.33	$57.35	$57.30
Purchase #4	$168.72	12.302%	$189.4759	$189.48	$189.50	$189.50
Purchase #5	$118.93	12.231%	$133.4763	$133.48	$133.50	$133.50
Purchase #6	$217.69	11.690%	$243.138	$243.14	$243.15	$243.10
Purchase #7	$54.79	5.626%	$57.8725	$57.87	$57.85	$57.90
7 purchase totals =	$894.58		$1,002.3999	$1,002.41	$1,002.45	$1,002.40