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	$117.89	11.684%	$131.6643	$131.66	$131.65	$131.70
Purchase #2	$176.92	10.687%	$195.8274	$195.83	$195.85	$195.80
Purchase #3	$46.31	8.118%	$50.0694	$50.07	$50.05	$50.10
Purchase #4	$46.71	9.274%	$51.0419	$51.04	$51.05	$51.00
Purchase #5	$168.59	12.303%	$189.3316	$189.33	$189.35	$189.30
Purchase #6	$162.94	11.616%	$181.8671	$181.87	$181.85	$181.90
Purchase #7	$108.68	13.480%	$123.3301	$123.33	$123.35	$123.30
7 purchase totals =	$828.04		$923.1318	$923.13	$923.15	$923.10