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	$203.27	11.870%	$227.3981	$227.40	$227.40	$227.40
Purchase #2	$113.32	12.805%	$127.8306	$127.83	$127.85	$127.80
Purchase #3	$185.37	10.833%	$205.4511	$205.45	$205.45	$205.50
Purchase #4	$137.53	12.257%	$154.3871	$154.39	$154.40	$154.40
Purchase #5	$239.56	12.279%	$268.9756	$268.98	$269.00	$269.00
Purchase #6	$66.41	8.738%	$72.2129	$72.21	$72.20	$72.20
Purchase #7	$174.96	12.245%	$196.3839	$196.38	$196.40	$196.40
7 purchase totals =	$1,120.42		$1,252.6393	$1,252.64	$1,252.70	$1,252.70