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	$142.27	12.556%	$160.1334	$160.13	$160.15	$160.10
Purchase #2	$87.73	12.787%	$98.948	$98.95	$98.95	$98.90
Purchase #3	$63.45	12.742%	$71.5348	$71.53	$71.55	$71.50
Purchase #4	$136.39	11.532%	$152.1185	$152.12	$152.10	$152.10
Purchase #5	$223.79	7.249%	$240.0125	$240.01	$240.00	$240.00
Purchase #6	$103.88	11.695%	$116.0288	$116.03	$116.05	$116.00
Purchase #7	$249.87	3.803%	$259.3726	$259.37	$259.35	$259.40
7 purchase totals =	$1,007.38		$1,098.1486	$1,098.14	$1,098.15	$1,098.00