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	$67.52	8.397%	$73.1897	$73.19	$73.20	$73.20
Purchase #2	$235.79	13.517%	$267.6617	$267.66	$267.65	$267.70
Purchase #3	$49.60	13.726%	$56.4081	$56.41	$56.40	$56.40
Purchase #4	$171.60	7.825%	$185.0277	$185.03	$185.05	$185.00
Purchase #5	$89.53	11.380%	$99.7185	$99.72	$99.70	$99.70
Purchase #6	$41.98	6.492%	$44.7053	$44.71	$44.70	$44.70
Purchase #7	$115.43	6.750%	$123.2215	$123.22	$123.20	$123.20
7 purchase totals =	$771.45		$849.9325	$849.94	$849.90	$849.90