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	$113.95	8.844%	$124.0277	$124.03	$124.05	$124.00
Purchase #2	$139.52	9.818%	$153.2181	$153.22	$153.20	$153.20
Purchase #3	$86.65	11.451%	$96.5723	$96.57	$96.55	$96.60
Purchase #4	$197.38	6.670%	$210.5452	$210.55	$210.55	$210.50
Purchase #5	$104.84	4.369%	$109.4205	$109.42	$109.40	$109.40
Purchase #6	$181.90	8.130%	$196.6885	$196.69	$196.70	$196.70
Purchase #7	$178.84	11.544%	$199.4853	$199.49	$199.50	$199.50
7 purchase totals =	$1,003.08		$1,089.9576	$1,089.97	$1,089.95	$1,089.90