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	$30.45	4.724%	$31.8885	$31.89	$31.90	$31.90
Purchase #2	$169.34	7.272%	$181.6544	$181.65	$181.65	$181.70
Purchase #3	$187.70	3.815%	$194.8608	$194.86	$194.85	$194.90
Purchase #4	$234.71	7.139%	$251.4659	$251.47	$251.45	$251.50
Purchase #5	$118.47	7.430%	$127.2723	$127.27	$127.25	$127.30
Purchase #6	$157.33	10.814%	$174.3437	$174.34	$174.35	$174.30
Purchase #7	$73.45	11.229%	$81.6977	$81.70	$81.70	$81.70
7 purchase totals =	$971.45		$1,043.1833	$1,043.18	$1,043.15	$1,043.30