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	$41.76	11.654%	$46.6267	$46.63	$46.65	$46.60
Purchase #2	$135.40	3.849%	$140.6115	$140.61	$140.60	$140.60
Purchase #3	$55.90	11.546%	$62.3542	$62.35	$62.35	$62.40
Purchase #4	$41.71	5.331%	$43.9336	$43.93	$43.95	$43.90
Purchase #5	$12.59	9.154%	$13.7425	$13.74	$13.75	$13.70
Purchase #6	$130.59	9.291%	$142.7231	$142.72	$142.70	$142.70
Purchase #7	$98.74	5.764%	$104.4314	$104.43	$104.45	$104.40
7 purchase totals =	$516.69		$554.4230	$554.41	$554.45	$554.30