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	$83.47	9.834%	$91.6784	$91.68	$91.70	$91.70
Purchase #2	$63.86	13.160%	$72.264	$72.26	$72.25	$72.30
Purchase #3	$218.84	9.351%	$239.3037	$239.30	$239.30	$239.30
Purchase #4	$167.84	5.410%	$176.9201	$176.92	$176.90	$176.90
Purchase #5	$163.83	4.739%	$171.5939	$171.59	$171.60	$171.60
Purchase #6	$70.82	13.549%	$80.4154	$80.42	$80.40	$80.40
Purchase #7	$151.96	12.717%	$171.2848	$171.28	$171.30	$171.30
7 purchase totals =	$920.62		$1,003.4603	$1,003.45	$1,003.45	$1,003.50