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	$91.45	4.658%	$95.7097	$95.71	$95.70	$95.70
Purchase #2	$170.76	4.485%	$178.4186	$178.42	$178.40	$178.40
Purchase #3	$238.47	5.220%	$250.9181	$250.92	$250.90	$250.90
Purchase #4	$154.62	9.525%	$169.3476	$169.35	$169.35	$169.30
Purchase #5	$113.50	8.626%	$123.2905	$123.29	$123.30	$123.30
Purchase #6	$77.79	6.796%	$83.0766	$83.08	$83.10	$83.10
Purchase #7	$155.46	13.315%	$176.1595	$176.16	$176.15	$176.20
7 purchase totals =	$1,002.05		$1,076.9206	$1,076.93	$1,076.90	$1,076.90