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	$28.81	13.781%	$32.7803	$32.78	$32.80	$32.80
Purchase #2	$247.84	7.756%	$267.0625	$267.06	$267.05	$267.10
Purchase #3	$64.80	9.576%	$71.0052	$71.01	$71.00	$71.00
Purchase #4	$138.64	6.233%	$147.2814	$147.28	$147.30	$147.30
Purchase #5	$57.72	3.681%	$59.8447	$59.84	$59.85	$59.80
Purchase #6	$64.33	9.164%	$70.2252	$70.23	$70.25	$70.20
Purchase #7	$151.76	9.422%	$166.0588	$166.06	$166.05	$166.10
7 purchase totals =	$753.90		$814.2581	$814.26	$814.30	$814.30