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	$35.72	5.715%	$37.7614	$37.76	$37.75	$37.80
Purchase #2	$127.40	4.700%	$133.3878	$133.39	$133.40	$133.40
Purchase #3	$162.54	10.720%	$179.9643	$179.96	$179.95	$180.00
Purchase #4	$87.78	4.179%	$91.4483	$91.45	$91.45	$91.40
Purchase #5	$71.94	7.155%	$77.0873	$77.09	$77.10	$77.10
Purchase #6	$145.86	5.742%	$154.2353	$154.24	$154.25	$154.20
Purchase #7	$82.54	11.340%	$91.9	$91.90	$91.90	$91.90
7 purchase totals =	$713.78		$765.7844	$765.79	$765.80	$765.80