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	$5.59	11.384%	$6.2264	$6.23	$6.25	$6.20
Purchase #2	$123.62	13.181%	$139.9144	$139.91	$139.90	$139.90
Purchase #3	$33.51	9.688%	$36.7564	$36.76	$36.75	$36.80
Purchase #4	$49.74	10.599%	$55.0119	$55.01	$55.00	$55.00
Purchase #5	$66.60	7.738%	$71.7535	$71.75	$71.75	$71.80
Purchase #6	$211.31	7.578%	$227.3231	$227.32	$227.30	$227.30
Purchase #7	$136.34	5.732%	$144.155	$144.16	$144.15	$144.20
7 purchase totals =	$626.71		$681.1407	$681.14	$681.10	$681.20