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	$215.77	12.564%	$242.8793	$242.88	$242.90	$242.90
Purchase #2	$175.68	11.769%	$196.3558	$196.36	$196.35	$196.40
Purchase #3	$106.72	12.852%	$120.4357	$120.44	$120.45	$120.40
Purchase #4	$206.26	13.347%	$233.7895	$233.79	$233.80	$233.80
Purchase #5	$248.66	12.460%	$279.643	$279.64	$279.65	$279.60
Purchase #6	$73.39	6.678%	$78.291	$78.29	$78.30	$78.30
Purchase #7	$12.29	6.223%	$13.0548	$13.05	$13.05	$13.10
7 purchase totals =	$1,038.77		$1,164.4491	$1,164.45	$1,164.50	$1,164.50