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	$55.68	5.873%	$58.9501	$58.95	$58.95	$59.00
Purchase #2	$173.70	8.689%	$188.7928	$188.79	$188.80	$188.80
Purchase #3	$86.54	10.736%	$95.8309	$95.83	$95.85	$95.80
Purchase #4	$206.84	10.619%	$228.8043	$228.80	$228.80	$228.80
Purchase #5	$130.85	10.404%	$144.4636	$144.46	$144.45	$144.50
Purchase #6	$120.98	8.441%	$131.1919	$131.19	$131.20	$131.20
Purchase #7	$80.47	11.637%	$89.8343	$89.83	$89.85	$89.80
7 purchase totals =	$855.06		$937.8679	$937.85	$937.90	$937.90