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	$135.40	13.781%	$154.0595	$154.06	$154.05	$154.10
Purchase #2	$179.60	11.838%	$200.861	$200.86	$200.85	$200.90
Purchase #3	$238.64	10.849%	$264.5301	$264.53	$264.55	$264.50
Purchase #4	$178.81	3.471%	$185.0165	$185.02	$185.00	$185.00
Purchase #5	$75.26	8.594%	$81.7278	$81.73	$81.75	$81.70
Purchase #6	$91.54	10.250%	$100.9229	$100.92	$100.90	$100.90
Purchase #7	$185.30	6.216%	$196.8182	$196.82	$196.80	$196.80
7 purchase totals =	$1,084.55		$1,183.9360	$1,183.94	$1,183.90	$1,183.90