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	$78.25	6.145%	$83.0585	$83.06	$83.05	$83.10
Purchase #2	$37.26	12.738%	$42.0062	$42.01	$42.00	$42.00
Purchase #3	$140.94	4.452%	$147.2146	$147.21	$147.20	$147.20
Purchase #4	$99.78	11.493%	$111.2477	$111.25	$111.25	$111.20
Purchase #5	$57.91	9.158%	$63.2134	$63.21	$63.20	$63.20
Purchase #6	$27.99	10.811%	$31.016	$31.02	$31.00	$31.00
Purchase #7	$241.63	4.843%	$253.3321	$253.33	$253.35	$253.30
7 purchase totals =	$683.76		$731.0885	$731.09	$731.05	$731.00