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	$129.41	6.238%	$137.4826	$137.48	$137.50	$137.50
Purchase #2	$186.84	5.109%	$196.3857	$196.39	$196.40	$196.40
Purchase #3	$215.80	13.115%	$244.1022	$244.10	$244.10	$244.10
Purchase #4	$164.72	12.844%	$185.8766	$185.88	$185.90	$185.90
Purchase #5	$134.51	6.701%	$143.5235	$143.52	$143.50	$143.50
Purchase #6	$244.75	8.123%	$264.631	$264.63	$264.65	$264.60
Purchase #7	$113.93	6.776%	$121.6499	$121.65	$121.65	$121.60
7 purchase totals =	$1,189.96		$1,293.6515	$1,293.65	$1,293.70	$1,293.60