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	$131.28	8.562%	$142.5202	$142.52	$142.50	$142.50
Purchase #2	$80.50	10.394%	$88.8672	$88.87	$88.85	$88.90
Purchase #3	$99.66	6.282%	$105.9206	$105.92	$105.90	$105.90
Purchase #4	$57.43	5.690%	$60.6978	$60.70	$60.70	$60.70
Purchase #5	$172.38	3.822%	$178.9684	$178.97	$178.95	$179.00
Purchase #6	$141.26	10.406%	$155.9595	$155.96	$155.95	$156.00
Purchase #7	$203.44	9.862%	$223.5033	$223.50	$223.50	$223.50
7 purchase totals =	$885.95		$956.4370	$956.44	$956.35	$956.50