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	$240.77	3.799%	$249.9169	$249.92	$249.90	$249.90
Purchase #2	$103.29	3.120%	$106.5126	$106.51	$106.50	$106.50
Purchase #3	$75.53	11.874%	$84.4984	$84.50	$84.50	$84.50
Purchase #4	$114.74	11.485%	$127.9179	$127.92	$127.90	$127.90
Purchase #5	$179.38	9.649%	$196.6884	$196.69	$196.70	$196.70
Purchase #6	$140.60	10.386%	$155.2027	$155.20	$155.20	$155.20
Purchase #7	$150.41	4.309%	$156.8912	$156.89	$156.90	$156.90
7 purchase totals =	$1,004.72		$1,077.6281	$1,077.63	$1,077.60	$1,077.60