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	$37.89	5.778%	$40.0793	$40.08	$40.10	$40.10
Purchase #2	$65.28	4.432%	$68.1732	$68.17	$68.15	$68.20
Purchase #3	$86.66	12.756%	$97.7143	$97.71	$97.70	$97.70
Purchase #4	$168.80	9.775%	$185.3002	$185.30	$185.30	$185.30
Purchase #5	$126.72	12.137%	$142.1	$142.10	$142.10	$142.10
Purchase #6	$65.54	3.337%	$67.7271	$67.73	$67.75	$67.70
Purchase #7	$103.35	9.641%	$113.314	$113.31	$113.30	$113.30
7 purchase totals =	$654.24		$714.4081	$714.40	$714.40	$714.40