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	$76.78	8.161%	$83.046	$83.05	$83.05	$83.00
Purchase #2	$10.26	4.385%	$10.7099	$10.71	$10.70	$10.70
Purchase #3	$245.94	11.349%	$273.8517	$273.85	$273.85	$273.90
Purchase #4	$91.57	12.427%	$102.9494	$102.95	$102.95	$102.90
Purchase #5	$16.90	9.112%	$18.4399	$18.44	$18.45	$18.40
Purchase #6	$17.78	5.257%	$18.7147	$18.71	$18.70	$18.70
Purchase #7	$100.55	4.309%	$104.8827	$104.88	$104.90	$104.90
7 purchase totals =	$559.78		$612.5943	$612.59	$612.60	$612.50