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	$243.99	13.752%	$277.5435	$277.54	$277.55	$277.50
Purchase #2	$165.48	12.647%	$186.4083	$186.41	$186.40	$186.40
Purchase #3	$116.52	9.759%	$127.8912	$127.89	$127.90	$127.90
Purchase #4	$240.66	12.347%	$270.3743	$270.37	$270.35	$270.40
Purchase #5	$186.89	7.513%	$200.931	$200.93	$200.95	$200.90
Purchase #6	$23.25	12.330%	$26.1167	$26.12	$26.10	$26.10
Purchase #7	$95.93	5.149%	$100.8694	$100.87	$100.85	$100.90
7 purchase totals =	$1,072.72		$1,190.1344	$1,190.13	$1,190.10	$1,190.10