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	$234.37	13.448%	$265.8881	$265.89	$265.90	$265.90
Purchase #2	$167.30	10.535%	$184.9251	$184.93	$184.95	$184.90
Purchase #3	$170.72	11.149%	$189.7536	$189.75	$189.75	$189.80
Purchase #4	$213.40	9.597%	$233.88	$233.88	$233.90	$233.90
Purchase #5	$220.87	8.713%	$240.1144	$240.11	$240.10	$240.10
Purchase #6	$73.82	6.107%	$78.3282	$78.33	$78.35	$78.30
Purchase #7	$5.54	8.483%	$6.01	$6.01	$6.00	$6.00
7 purchase totals =	$1,086.02		$1,198.8994	$1,198.90	$1,198.95	$1,198.90