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	$100.67	3.337%	$104.0294	$104.03	$104.05	$104.00
Purchase #2	$79.42	7.777%	$85.5965	$85.60	$85.60	$85.60
Purchase #3	$144.33	11.589%	$161.0564	$161.06	$161.05	$161.10
Purchase #4	$106.88	5.759%	$113.0352	$113.04	$113.05	$113.00
Purchase #5	$47.91	5.452%	$50.5221	$50.52	$50.50	$50.50
Purchase #6	$55.51	12.693%	$62.5559	$62.56	$62.55	$62.60
Purchase #7	$27.43	4.340%	$28.6205	$28.62	$28.60	$28.60
7 purchase totals =	$562.15		$605.4160	$605.43	$605.40	$605.40