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	$11.49	9.787%	$12.6145	$12.61	$12.60	$12.60
Purchase #2	$125.50	12.516%	$141.2076	$141.21	$141.20	$141.20
Purchase #3	$88.81	10.431%	$98.0738	$98.07	$98.05	$98.10
Purchase #4	$93.38	8.814%	$101.6105	$101.61	$101.60	$101.60
Purchase #5	$162.36	10.404%	$179.2519	$179.25	$179.25	$179.30
Purchase #6	$66.39	9.711%	$72.8371	$72.84	$72.85	$72.80
Purchase #7	$181.93	4.362%	$189.8658	$189.87	$189.85	$189.90
7 purchase totals =	$729.86		$795.4612	$795.46	$795.40	$795.50