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	$44.88	13.576%	$50.9729	$50.97	$50.95	$51.00
Purchase #2	$144.81	12.133%	$162.3798	$162.38	$162.40	$162.40
Purchase #3	$164.90	12.511%	$185.5306	$185.53	$185.55	$185.50
Purchase #4	$33.92	11.660%	$37.8751	$37.88	$37.90	$37.90
Purchase #5	$244.59	3.769%	$253.8086	$253.81	$253.80	$253.80
Purchase #6	$78.56	6.612%	$83.7544	$83.75	$83.75	$83.80
Purchase #7	$27.29	8.790%	$29.6888	$29.69	$29.70	$29.70
7 purchase totals =	$738.95		$804.0102	$804.01	$804.05	$804.10