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	$138.64	12.529%	$156.0102	$156.01	$156.00	$156.00
Purchase #2	$134.67	3.578%	$139.4885	$139.49	$139.50	$139.50
Purchase #3	$161.87	13.767%	$184.1546	$184.15	$184.15	$184.20
Purchase #4	$51.51	13.136%	$58.2764	$58.28	$58.30	$58.30
Purchase #5	$110.44	12.122%	$123.8275	$123.83	$123.85	$123.80
Purchase #6	$218.27	4.107%	$227.2343	$227.23	$227.25	$227.20
Purchase #7	$55.45	7.272%	$59.4823	$59.48	$59.50	$59.50
7 purchase totals =	$870.85		$948.4738	$948.47	$948.55	$948.50