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	$170.83	6.279%	$181.5564	$181.56	$181.55	$181.60
Purchase #2	$20.56	7.721%	$22.1474	$22.15	$22.15	$22.10
Purchase #3	$128.57	6.625%	$137.0878	$137.09	$137.10	$137.10
Purchase #4	$93.96	7.238%	$100.7608	$100.76	$100.75	$100.80
Purchase #5	$174.77	6.614%	$186.3293	$186.33	$186.35	$186.30
Purchase #6	$29.59	6.542%	$31.5258	$31.53	$31.55	$31.50
Purchase #7	$214.47	4.103%	$223.2697	$223.27	$223.25	$223.30
7 purchase totals =	$832.75		$882.6772	$882.69	$882.70	$882.70