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	$28.39	12.330%	$31.8905	$31.89	$31.90	$31.90
Purchase #2	$59.57	4.632%	$62.3293	$62.33	$62.35	$62.30
Purchase #3	$190.69	13.776%	$216.9595	$216.96	$216.95	$217.00
Purchase #4	$143.40	7.155%	$153.6603	$153.66	$153.65	$153.70
Purchase #5	$47.36	10.464%	$52.3158	$52.32	$52.30	$52.30
Purchase #6	$188.57	4.427%	$196.918	$196.92	$196.90	$196.90
Purchase #7	$214.67	9.809%	$235.727	$235.73	$235.75	$235.70
7 purchase totals =	$872.65		$949.8004	$949.81	$949.80	$949.80