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	$25.78	8.467%	$27.9628	$27.96	$27.95	$28.00
Purchase #2	$211.98	12.781%	$239.0732	$239.07	$239.05	$239.10
Purchase #3	$219.70	13.458%	$249.2672	$249.27	$249.25	$249.30
Purchase #4	$167.53	4.518%	$175.099	$175.10	$175.10	$175.10
Purchase #5	$245.41	4.265%	$255.8767	$255.88	$255.90	$255.90
Purchase #6	$59.52	11.354%	$66.2779	$66.28	$66.30	$66.30
Purchase #7	$181.81	10.457%	$200.8219	$200.82	$200.80	$200.80
7 purchase totals =	$1,111.73		$1,214.3787	$1,214.38	$1,214.35	$1,214.50