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	$167.43	7.611%	$180.1731	$180.17	$180.15	$180.20
Purchase #2	$173.30	10.525%	$191.5398	$191.54	$191.55	$191.50
Purchase #3	$144.76	7.642%	$155.8226	$155.82	$155.80	$155.80
Purchase #4	$225.73	6.426%	$240.2354	$240.24	$240.25	$240.20
Purchase #5	$201.50	6.769%	$215.1395	$215.14	$215.15	$215.10
Purchase #6	$127.78	9.197%	$139.5319	$139.53	$139.55	$139.50
Purchase #7	$237.37	12.784%	$267.7154	$267.72	$267.70	$267.70
7 purchase totals =	$1,277.87		$1,390.1577	$1,390.16	$1,390.15	$1,390.00