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	$75.40	3.506%	$78.0435	$78.04	$78.05	$78.00
Purchase #2	$208.39	12.520%	$234.4804	$234.48	$234.50	$234.50
Purchase #3	$141.74	9.505%	$155.2124	$155.21	$155.20	$155.20
Purchase #4	$169.62	9.287%	$185.3726	$185.37	$185.35	$185.40
Purchase #5	$54.51	8.850%	$59.3341	$59.33	$59.35	$59.30
Purchase #6	$187.86	8.162%	$203.1931	$203.19	$203.20	$203.20
Purchase #7	$176.32	5.377%	$185.8007	$185.80	$185.80	$185.80
7 purchase totals =	$1,013.84		$1,101.4368	$1,101.42	$1,101.45	$1,101.40