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	$166.96	8.453%	$181.0731	$181.07	$181.05	$181.10
Purchase #2	$95.43	8.853%	$103.8784	$103.88	$103.90	$103.90
Purchase #3	$117.63	11.156%	$130.7528	$130.75	$130.75	$130.80
Purchase #4	$72.77	13.239%	$82.404	$82.40	$82.40	$82.40
Purchase #5	$79.71	11.747%	$89.0735	$89.07	$89.05	$89.10
Purchase #6	$206.36	4.720%	$216.1002	$216.10	$216.10	$216.10
Purchase #7	$34.75	4.296%	$36.2429	$36.24	$36.25	$36.20
7 purchase totals =	$773.61		$839.5249	$839.51	$839.50	$839.60