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	$87.91	12.590%	$98.9779	$98.98	$99.00	$99.00
Purchase #2	$164.30	7.323%	$176.3317	$176.33	$176.35	$176.30
Purchase #3	$121.27	7.559%	$130.4368	$130.44	$130.45	$130.40
Purchase #4	$59.77	4.186%	$62.272	$62.27	$62.25	$62.30
Purchase #5	$140.44	10.800%	$155.6075	$155.61	$155.60	$155.60
Purchase #6	$107.86	12.112%	$120.924	$120.92	$120.90	$120.90
Purchase #7	$232.70	13.174%	$263.3559	$263.36	$263.35	$263.40
7 purchase totals =	$914.25		$1,007.9058	$1,007.91	$1,007.90	$1,007.90