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	$168.28	9.648%	$184.5157	$184.52	$184.50	$184.50
Purchase #2	$74.56	10.652%	$82.5021	$82.50	$82.50	$82.50
Purchase #3	$73.44	7.817%	$79.1808	$79.18	$79.20	$79.20
Purchase #4	$198.51	6.210%	$210.8375	$210.84	$210.85	$210.80
Purchase #5	$164.89	6.370%	$175.3935	$175.39	$175.40	$175.40
Purchase #6	$47.67	11.787%	$53.2889	$53.29	$53.30	$53.30
Purchase #7	$117.50	12.249%	$131.8926	$131.89	$131.90	$131.90
7 purchase totals =	$844.85		$917.6111	$917.61	$917.65	$917.60