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	$53.97	3.331%	$55.7677	$55.77	$55.75	$55.80
Purchase #2	$44.31	6.453%	$47.1693	$47.17	$47.15	$47.20
Purchase #3	$90.84	12.552%	$102.2422	$102.24	$102.25	$102.20
Purchase #4	$191.80	11.834%	$214.4976	$214.50	$214.50	$214.50
Purchase #5	$108.34	4.107%	$112.7895	$112.79	$112.80	$112.80
Purchase #6	$53.86	9.790%	$59.1329	$59.13	$59.15	$59.10
Purchase #7	$65.36	11.529%	$72.8954	$72.90	$72.90	$72.90
7 purchase totals =	$608.48		$664.4946	$664.50	$664.50	$664.50