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	$131.79	10.781%	$145.9983	$146.00	$146.00	$146.00
Purchase #2	$119.86	5.638%	$126.6177	$126.62	$126.60	$126.60
Purchase #3	$161.25	6.331%	$171.4587	$171.46	$171.45	$171.50
Purchase #4	$28.61	11.658%	$31.9454	$31.95	$31.95	$31.90
Purchase #5	$87.78	11.524%	$97.8958	$97.90	$97.90	$97.90
Purchase #6	$228.44	11.772%	$255.332	$255.33	$255.35	$255.30
Purchase #7	$91.56	9.135%	$99.924	$99.92	$99.90	$99.90
7 purchase totals =	$849.29		$929.1719	$929.18	$929.15	$929.10