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	$89.41	8.213%	$96.7532	$96.75	$96.75	$96.80
Purchase #2	$239.31	4.365%	$249.7559	$249.76	$249.75	$249.80
Purchase #3	$181.37	8.184%	$196.2133	$196.21	$196.20	$196.20
Purchase #4	$82.84	5.569%	$87.4534	$87.45	$87.45	$87.50
Purchase #5	$115.51	10.718%	$127.8904	$127.89	$127.90	$127.90
Purchase #6	$240.44	10.742%	$266.2681	$266.27	$266.25	$266.30
Purchase #7	$201.87	8.352%	$218.7302	$218.73	$218.75	$218.70
7 purchase totals =	$1,150.75		$1,243.0645	$1,243.06	$1,243.05	$1,243.20