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	$181.49	3.185%	$187.2705	$187.27	$187.25	$187.30
Purchase #2	$50.83	11.407%	$56.6282	$56.63	$56.65	$56.60
Purchase #3	$180.89	4.520%	$189.0662	$189.07	$189.05	$189.10
Purchase #4	$226.36	5.346%	$238.4612	$238.46	$238.45	$238.50
Purchase #5	$68.49	8.740%	$74.476	$74.48	$74.50	$74.50
Purchase #6	$88.38	11.525%	$98.5658	$98.57	$98.55	$98.60
Purchase #7	$42.37	8.183%	$45.8371	$45.84	$45.85	$45.80
7 purchase totals =	$838.81		$890.3050	$890.32	$890.30	$890.40