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	$109.98	12.614%	$123.8529	$123.85	$123.85	$123.90
Purchase #2	$42.57	11.411%	$47.4277	$47.43	$47.45	$47.40
Purchase #3	$201.51	4.439%	$210.455	$210.46	$210.45	$210.50
Purchase #4	$109.51	5.714%	$115.7674	$115.77	$115.75	$115.80
Purchase #5	$59.40	9.336%	$64.9456	$64.95	$64.95	$64.90
Purchase #6	$25.41	8.788%	$27.643	$27.64	$27.65	$27.60
Purchase #7	$204.80	8.642%	$222.4988	$222.50	$222.50	$222.50
7 purchase totals =	$753.18		$812.5904	$812.60	$812.60	$812.60