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	$82.30	10.421%	$90.8765	$90.88	$90.90	$90.90
Purchase #2	$208.56	12.645%	$234.9324	$234.93	$234.95	$234.90
Purchase #3	$238.95	11.302%	$265.9561	$265.96	$265.95	$266.00
Purchase #4	$70.78	6.191%	$75.162	$75.16	$75.15	$75.20
Purchase #5	$79.80	12.788%	$90.0048	$90.00	$90.00	$90.00
Purchase #6	$240.47	12.618%	$270.8125	$270.81	$270.80	$270.80
Purchase #7	$52.64	6.346%	$55.9805	$55.98	$56.00	$56.00
7 purchase totals =	$973.50		$1,083.7248	$1,083.72	$1,083.75	$1,083.80