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	$190.38	11.832%	$212.9058	$212.91	$212.90	$212.90
Purchase #2	$45.94	9.356%	$50.2381	$50.24	$50.25	$50.20
Purchase #3	$144.50	12.479%	$162.5322	$162.53	$162.55	$162.50
Purchase #4	$47.69	7.269%	$51.1566	$51.16	$51.15	$51.20
Purchase #5	$113.55	8.338%	$123.0178	$123.02	$123.00	$123.00
Purchase #6	$86.61	9.761%	$95.064	$95.06	$95.05	$95.10
Purchase #7	$111.96	7.203%	$120.0245	$120.02	$120.00	$120.00
7 purchase totals =	$740.63		$814.9390	$814.94	$814.90	$814.90