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	$75.61	12.509%	$85.0681	$85.07	$85.05	$85.10
Purchase #2	$31.83	5.471%	$33.5714	$33.57	$33.55	$33.60
Purchase #3	$154.50	9.487%	$169.1574	$169.16	$169.15	$169.20
Purchase #4	$209.97	6.428%	$223.4669	$223.47	$223.45	$223.50
Purchase #5	$221.76	12.866%	$250.2916	$250.29	$250.30	$250.30
Purchase #6	$77.37	6.569%	$82.4524	$82.45	$82.45	$82.50
Purchase #7	$78.31	10.580%	$86.5952	$86.60	$86.60	$86.60
7 purchase totals =	$849.35		$930.6030	$930.61	$930.55	$930.80