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	$35.74	13.308%	$40.4963	$40.50	$40.50	$40.50
Purchase #2	$77.43	10.607%	$85.643	$85.64	$85.65	$85.60
Purchase #3	$40.34	4.750%	$42.2562	$42.26	$42.25	$42.30
Purchase #4	$248.86	11.769%	$278.1483	$278.15	$278.15	$278.10
Purchase #5	$204.95	6.719%	$218.7206	$218.72	$218.70	$218.70
Purchase #6	$33.59	9.454%	$36.7656	$36.77	$36.75	$36.80
Purchase #7	$85.37	4.296%	$89.0375	$89.04	$89.05	$89.00
7 purchase totals =	$726.28		$791.0675	$791.08	$791.05	$791.00