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	$56.57	4.369%	$59.0415	$59.04	$59.05	$59.00
Purchase #2	$59.42	10.214%	$65.4892	$65.49	$65.50	$65.50
Purchase #3	$205.36	13.416%	$232.9111	$232.91	$232.90	$232.90
Purchase #4	$72.91	9.848%	$80.0902	$80.09	$80.10	$80.10
Purchase #5	$75.50	10.122%	$83.1421	$83.14	$83.15	$83.10
Purchase #6	$78.38	12.350%	$88.0599	$88.06	$88.05	$88.10
Purchase #7	$246.37	10.347%	$271.8619	$271.86	$271.85	$271.90
7 purchase totals =	$794.51		$880.5959	$880.59	$880.60	$880.60