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	$156.26	7.709%	$168.3061	$168.31	$168.30	$168.30
Purchase #2	$194.82	7.339%	$209.1178	$209.12	$209.10	$209.10
Purchase #3	$142.72	8.138%	$154.3346	$154.33	$154.35	$154.30
Purchase #4	$133.70	11.197%	$148.6704	$148.67	$148.65	$148.70
Purchase #5	$198.68	12.193%	$222.9051	$222.91	$222.90	$222.90
Purchase #6	$210.55	5.850%	$222.8672	$222.87	$222.85	$222.90
Purchase #7	$124.73	9.125%	$136.1116	$136.11	$136.10	$136.10
7 purchase totals =	$1,161.46		$1,262.3128	$1,262.32	$1,262.25	$1,262.30