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	$97.31	6.308%	$103.4483	$103.45	$103.45	$103.40
Purchase #2	$36.91	9.533%	$40.4286	$40.43	$40.45	$40.40
Purchase #3	$182.72	10.517%	$201.9367	$201.94	$201.95	$201.90
Purchase #4	$195.57	12.431%	$219.8813	$219.88	$219.90	$219.90
Purchase #5	$70.27	12.213%	$78.8521	$78.85	$78.85	$78.90
Purchase #6	$208.61	12.169%	$233.9958	$234.00	$234.00	$234.00
Purchase #7	$144.63	12.362%	$162.5092	$162.51	$162.50	$162.50
7 purchase totals =	$936.02		$1,041.0520	$1,041.06	$1,041.10	$1,041.00