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	$9.88	4.169%	$10.2919	$10.29	$10.30	$10.30
Purchase #2	$204.44	9.375%	$223.6063	$223.61	$223.60	$223.60
Purchase #3	$116.66	9.833%	$128.1312	$128.13	$128.15	$128.10
Purchase #4	$58.33	4.165%	$60.7594	$60.76	$60.75	$60.80
Purchase #5	$225.46	3.807%	$234.0433	$234.04	$234.05	$234.00
Purchase #6	$20.78	3.769%	$21.5632	$21.56	$21.55	$21.60
Purchase #7	$117.46	11.571%	$131.0513	$131.05	$131.05	$131.10
7 purchase totals =	$753.01		$809.4466	$809.44	$809.45	$809.50