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	$21.96	13.453%	$24.9143	$24.91	$24.90	$24.90
Purchase #2	$43.40	7.787%	$46.7796	$46.78	$46.80	$46.80
Purchase #3	$6.44	6.608%	$6.8656	$6.87	$6.85	$6.90
Purchase #4	$222.89	3.836%	$231.4401	$231.44	$231.45	$231.40
Purchase #5	$133.54	9.338%	$146.01	$146.01	$146.00	$146.00
Purchase #6	$89.25	12.173%	$100.1144	$100.11	$100.10	$100.10
Purchase #7	$243.38	4.157%	$253.4973	$253.50	$253.50	$253.50
7 purchase totals =	$760.86		$809.6213	$809.62	$809.60	$809.60