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	$35.33	3.317%	$36.5019	$36.50	$36.50	$36.50
Purchase #2	$72.95	6.682%	$77.8245	$77.82	$77.80	$77.80
Purchase #3	$91.64	8.753%	$99.6612	$99.66	$99.65	$99.70
Purchase #4	$90.28	9.859%	$99.1807	$99.18	$99.20	$99.20
Purchase #5	$216.31	4.824%	$226.7448	$226.74	$226.75	$226.70
Purchase #6	$109.87	8.862%	$119.6067	$119.61	$119.60	$119.60
Purchase #7	$147.90	11.183%	$164.4397	$164.44	$164.45	$164.40
7 purchase totals =	$764.28		$823.9595	$823.95	$823.95	$823.90