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	$250.46	10.412%	$276.5379	$276.54	$276.55	$276.50
Purchase #2	$110.65	3.427%	$114.442	$114.44	$114.45	$114.40
Purchase #3	$32.98	13.669%	$37.488	$37.49	$37.50	$37.50
Purchase #4	$76.78	11.432%	$85.5575	$85.56	$85.55	$85.60
Purchase #5	$175.28	7.725%	$188.8204	$188.82	$188.80	$188.80
Purchase #6	$19.79	3.460%	$20.4747	$20.47	$20.45	$20.50
Purchase #7	$167.90	11.725%	$187.5863	$187.59	$187.60	$187.60
7 purchase totals =	$833.84		$910.9068	$910.91	$910.90	$910.90