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	$217.89	10.383%	$240.5135	$240.51	$240.50	$240.50
Purchase #2	$109.95	9.854%	$120.7845	$120.78	$120.80	$120.80
Purchase #3	$78.64	11.481%	$87.6687	$87.67	$87.65	$87.70
Purchase #4	$109.63	4.104%	$114.1292	$114.13	$114.15	$114.10
Purchase #5	$242.64	11.374%	$270.2379	$270.24	$270.25	$270.20
Purchase #6	$189.96	11.357%	$211.5338	$211.53	$211.55	$211.50
Purchase #7	$28.58	13.388%	$32.4063	$32.41	$32.40	$32.40
7 purchase totals =	$977.29		$1,077.2739	$1,077.27	$1,077.30	$1,077.20