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	$85.62	10.357%	$94.4877	$94.49	$94.50	$94.50
Purchase #2	$72.86	8.117%	$78.774	$78.77	$78.75	$78.80
Purchase #3	$67.84	6.134%	$72.0013	$72.00	$72.00	$72.00
Purchase #4	$56.77	8.161%	$61.403	$61.40	$61.40	$61.40
Purchase #5	$75.43	6.283%	$80.1693	$80.17	$80.15	$80.20
Purchase #6	$153.29	10.174%	$168.8857	$168.89	$168.90	$168.90
Purchase #7	$42.70	3.217%	$44.0737	$44.07	$44.05	$44.10
7 purchase totals =	$554.51		$599.7947	$599.79	$599.75	$599.90