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	$77.37	12.223%	$86.8269	$86.83	$86.85	$86.80
Purchase #2	$127.73	9.454%	$139.8056	$139.81	$139.80	$139.80
Purchase #3	$30.53	9.331%	$33.3788	$33.38	$33.40	$33.40
Purchase #4	$127.27	4.404%	$132.875	$132.88	$132.90	$132.90
Purchase #5	$160.82	13.372%	$182.3249	$182.32	$182.30	$182.30
Purchase #6	$100.56	9.717%	$110.3314	$110.33	$110.35	$110.30
Purchase #7	$210.46	9.298%	$230.0286	$230.03	$230.05	$230.00
7 purchase totals =	$834.74		$915.5712	$915.58	$915.65	$915.50