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	$6.77	12.273%	$7.6009	$7.60	$7.60	$7.60
Purchase #2	$50.76	4.102%	$52.8422	$52.84	$52.85	$52.80
Purchase #3	$242.41	13.419%	$274.939	$274.94	$274.95	$274.90
Purchase #4	$204.69	10.334%	$225.8427	$225.84	$225.85	$225.80
Purchase #5	$20.47	4.446%	$21.3801	$21.38	$21.40	$21.40
Purchase #6	$30.51	3.539%	$31.5897	$31.59	$31.60	$31.60
Purchase #7	$169.60	11.752%	$189.5314	$189.53	$189.55	$189.50
7 purchase totals =	$725.21		$803.7260	$803.72	$803.80	$803.60