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	$33.61	13.155%	$38.0314	$38.03	$38.05	$38.00
Purchase #2	$176.29	7.686%	$189.8396	$189.84	$189.85	$189.80
Purchase #3	$53.54	4.367%	$55.8781	$55.88	$55.90	$55.90
Purchase #4	$134.43	3.531%	$139.1767	$139.18	$139.20	$139.20
Purchase #5	$78.97	13.666%	$89.762	$89.76	$89.75	$89.80
Purchase #6	$231.98	13.203%	$262.6083	$262.61	$262.60	$262.60
Purchase #7	$147.50	13.608%	$167.5718	$167.57	$167.55	$167.60
7 purchase totals =	$856.32		$942.8679	$942.87	$942.90	$942.90