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	$121.39	8.638%	$131.8757	$131.88	$131.90	$131.90
Purchase #2	$176.61	12.370%	$198.4567	$198.46	$198.45	$198.50
Purchase #3	$197.27	6.751%	$210.5877	$210.59	$210.60	$210.60
Purchase #4	$93.97	11.819%	$105.0763	$105.08	$105.10	$105.10
Purchase #5	$154.50	7.241%	$165.6873	$165.69	$165.70	$165.70
Purchase #6	$59.33	9.820%	$65.1562	$65.16	$65.15	$65.20
Purchase #7	$120.98	6.403%	$128.7263	$128.73	$128.75	$128.70
7 purchase totals =	$924.05		$1,005.5662	$1,005.59	$1,005.65	$1,005.70