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	$73.56	12.713%	$82.9117	$82.91	$82.90	$82.90
Purchase #2	$248.37	11.543%	$277.0393	$277.04	$277.05	$277.00
Purchase #3	$173.89	4.680%	$182.0281	$182.03	$182.05	$182.00
Purchase #4	$40.93	12.530%	$46.0585	$46.06	$46.05	$46.10
Purchase #5	$201.32	8.843%	$219.1227	$219.12	$219.10	$219.10
Purchase #6	$63.31	12.339%	$71.1218	$71.12	$71.10	$71.10
Purchase #7	$106.85	5.168%	$112.372	$112.37	$112.35	$112.40
7 purchase totals =	$908.23		$990.6541	$990.65	$990.60	$990.60