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	$148.54	13.302%	$168.2988	$168.30	$168.30	$168.30
Purchase #2	$18.83	6.738%	$20.0988	$20.10	$20.10	$20.10
Purchase #3	$84.64	3.427%	$87.5406	$87.54	$87.55	$87.50
Purchase #4	$116.83	12.699%	$131.6662	$131.67	$131.65	$131.70
Purchase #5	$98.58	5.673%	$104.1724	$104.17	$104.15	$104.20
Purchase #6	$187.31	12.362%	$210.4653	$210.47	$210.45	$210.50
Purchase #7	$104.44	12.869%	$117.8804	$117.88	$117.90	$117.90
7 purchase totals =	$759.17		$840.1225	$840.13	$840.10	$840.20