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	$100.65	10.362%	$111.0794	$111.08	$111.10	$111.10
Purchase #2	$75.78	10.858%	$84.0082	$84.01	$84.00	$84.00
Purchase #3	$120.32	4.336%	$125.5371	$125.54	$125.55	$125.50
Purchase #4	$28.81	12.278%	$32.3473	$32.35	$32.35	$32.30
Purchase #5	$64.71	11.216%	$71.9679	$71.97	$71.95	$72.00
Purchase #6	$156.82	5.163%	$164.9166	$164.92	$164.90	$164.90
Purchase #7	$242.63	9.374%	$265.3741	$265.37	$265.35	$265.40
7 purchase totals =	$789.72		$855.2306	$855.24	$855.20	$855.20