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	$73.60	6.612%	$78.4664	$78.47	$78.45	$78.50
Purchase #2	$58.60	8.155%	$63.3788	$63.38	$63.40	$63.40
Purchase #3	$239.56	3.665%	$248.3399	$248.34	$248.35	$248.30
Purchase #4	$166.53	10.453%	$183.9374	$183.94	$183.95	$183.90
Purchase #5	$131.97	8.750%	$143.5174	$143.52	$143.50	$143.50
Purchase #6	$54.86	9.597%	$60.1249	$60.12	$60.10	$60.10
Purchase #7	$55.68	6.320%	$59.199	$59.20	$59.20	$59.20
7 purchase totals =	$780.80		$836.9638	$836.97	$836.95	$836.90