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	$36.60	7.447%	$39.3256	$39.33	$39.35	$39.30
Purchase #2	$241.83	10.657%	$267.6018	$267.60	$267.60	$267.60
Purchase #3	$139.46	8.498%	$151.3113	$151.31	$151.30	$151.30
Purchase #4	$131.48	5.740%	$139.027	$139.03	$139.05	$139.00
Purchase #5	$38.31	4.581%	$40.065	$40.07	$40.05	$40.10
Purchase #6	$92.43	12.625%	$104.0993	$104.10	$104.10	$104.10
Purchase #7	$62.97	7.313%	$67.575	$67.58	$67.60	$67.60
7 purchase totals =	$743.08		$809.0050	$809.02	$809.05	$809.00