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	$126.48	3.737%	$131.2066	$131.21	$131.20	$131.20
Purchase #2	$40.65	4.360%	$42.4223	$42.42	$42.40	$42.40
Purchase #3	$144.96	10.651%	$160.3997	$160.40	$160.40	$160.40
Purchase #4	$24.69	4.566%	$25.8173	$25.82	$25.80	$25.80
Purchase #5	$238.79	4.388%	$249.2681	$249.27	$249.25	$249.30
Purchase #6	$152.66	12.458%	$171.6784	$171.68	$171.70	$171.70
Purchase #7	$62.38	13.709%	$70.9317	$70.93	$70.95	$70.90
7 purchase totals =	$790.61		$851.7241	$851.73	$851.70	$851.70