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	$109.62	13.272%	$124.1688	$124.17	$124.15	$124.20
Purchase #2	$241.72	7.700%	$260.3324	$260.33	$260.35	$260.30
Purchase #3	$82.95	7.751%	$89.3795	$89.38	$89.40	$89.40
Purchase #4	$217.64	9.377%	$238.0481	$238.05	$238.05	$238.00
Purchase #5	$52.83	5.422%	$55.6944	$55.69	$55.70	$55.70
Purchase #6	$109.77	12.118%	$123.0719	$123.07	$123.05	$123.10
Purchase #7	$138.80	4.383%	$144.8836	$144.88	$144.90	$144.90
7 purchase totals =	$953.33		$1,035.5787	$1,035.57	$1,035.60	$1,035.60