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	$82.93	12.629%	$93.4032	$93.40	$93.40	$93.40
Purchase #2	$99.41	13.457%	$112.7876	$112.79	$112.80	$112.80
Purchase #3	$32.33	9.279%	$35.3299	$35.33	$35.35	$35.30
Purchase #4	$216.29	12.175%	$242.6233	$242.62	$242.60	$242.60
Purchase #5	$143.54	3.724%	$148.8854	$148.89	$148.90	$148.90
Purchase #6	$90.83	10.618%	$100.4743	$100.47	$100.45	$100.50
Purchase #7	$28.47	7.770%	$30.6821	$30.68	$30.70	$30.70
7 purchase totals =	$693.80		$764.1858	$764.18	$764.20	$764.20