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	$138.42	13.327%	$156.8672	$156.87	$156.85	$156.90
Purchase #2	$162.74	5.620%	$171.886	$171.89	$171.90	$171.90
Purchase #3	$90.75	6.806%	$96.9264	$96.93	$96.95	$96.90
Purchase #4	$33.95	10.454%	$37.4991	$37.50	$37.50	$37.50
Purchase #5	$176.91	13.592%	$200.9556	$200.96	$200.95	$201.00
Purchase #6	$129.99	12.541%	$146.292	$146.29	$146.30	$146.30
Purchase #7	$109.72	8.806%	$119.3819	$119.38	$119.40	$119.40
7 purchase totals =	$842.48		$929.8082	$929.82	$929.85	$929.90