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	$27.79	11.712%	$31.0448	$31.04	$31.05	$31.00
Purchase #2	$123.54	9.596%	$135.3949	$135.39	$135.40	$135.40
Purchase #3	$223.59	6.661%	$238.4833	$238.48	$238.50	$238.50
Purchase #4	$121.96	6.131%	$129.4374	$129.44	$129.45	$129.40
Purchase #5	$99.78	11.677%	$111.4313	$111.43	$111.45	$111.40
Purchase #6	$6.31	7.362%	$6.7745	$6.77	$6.75	$6.80
Purchase #7	$78.96	13.304%	$89.4648	$89.46	$89.45	$89.50
7 purchase totals =	$681.93		$742.0310	$742.01	$742.05	$742.00