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	$83.72	7.199%	$89.747	$89.75	$89.75	$89.70
Purchase #2	$242.46	9.250%	$264.8876	$264.89	$264.90	$264.90
Purchase #3	$139.73	12.287%	$156.8986	$156.90	$156.90	$156.90
Purchase #4	$144.60	8.524%	$156.9257	$156.93	$156.95	$156.90
Purchase #5	$232.72	3.781%	$241.5191	$241.52	$241.50	$241.50
Purchase #6	$212.89	13.585%	$241.8111	$241.81	$241.80	$241.80
Purchase #7	$108.94	12.573%	$122.637	$122.64	$122.65	$122.60
7 purchase totals =	$1,165.06		$1,274.4261	$1,274.44	$1,274.45	$1,274.30