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	$134.61	10.146%	$148.2675	$148.27	$148.25	$148.30
Purchase #2	$146.38	13.366%	$165.9452	$165.95	$165.95	$165.90
Purchase #3	$119.73	11.450%	$133.4391	$133.44	$133.45	$133.40
Purchase #4	$71.93	7.780%	$77.5262	$77.53	$77.55	$77.50
Purchase #5	$72.72	8.416%	$78.8401	$78.84	$78.85	$78.80
Purchase #6	$167.66	11.181%	$186.4061	$186.41	$186.40	$186.40
Purchase #7	$122.98	6.788%	$131.3279	$131.33	$131.35	$131.30
7 purchase totals =	$836.01		$921.7521	$921.77	$921.80	$921.60