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	$120.97	5.264%	$127.3379	$127.34	$127.35	$127.30
Purchase #2	$20.47	12.398%	$23.0079	$23.01	$23.00	$23.00
Purchase #3	$47.53	12.269%	$53.3615	$53.36	$53.35	$53.40
Purchase #4	$32.53	5.526%	$34.3276	$34.33	$34.35	$34.30
Purchase #5	$130.91	6.517%	$139.4414	$139.44	$139.45	$139.40
Purchase #6	$127.29	11.353%	$141.7412	$141.74	$141.75	$141.70
Purchase #7	$109.89	3.216%	$113.4241	$113.42	$113.40	$113.40
7 purchase totals =	$589.59		$632.6416	$632.64	$632.65	$632.50