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	$125.88	4.391%	$131.4074	$131.41	$131.40	$131.40
Purchase #2	$242.39	8.300%	$262.5084	$262.51	$262.50	$262.50
Purchase #3	$222.67	12.328%	$250.1208	$250.12	$250.10	$250.10
Purchase #4	$114.76	11.828%	$128.3338	$128.33	$128.35	$128.30
Purchase #5	$72.49	13.727%	$82.4407	$82.44	$82.45	$82.40
Purchase #6	$92.49	13.762%	$105.2185	$105.22	$105.20	$105.20
Purchase #7	$246.61	4.368%	$257.3819	$257.38	$257.40	$257.40
7 purchase totals =	$1,117.29		$1,217.4115	$1,217.41	$1,217.40	$1,217.30