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	$123.37	3.582%	$127.7891	$127.79	$127.80	$127.80
Purchase #2	$104.64	4.647%	$109.5026	$109.50	$109.50	$109.50
Purchase #3	$236.94	7.782%	$255.3787	$255.38	$255.40	$255.40
Purchase #4	$245.68	10.266%	$270.9015	$270.90	$270.90	$270.90
Purchase #5	$200.63	10.407%	$221.5096	$221.51	$221.50	$221.50
Purchase #6	$193.95	11.416%	$216.0913	$216.09	$216.10	$216.10
Purchase #7	$29.64	11.770%	$33.1286	$33.13	$33.15	$33.10
7 purchase totals =	$1,134.85		$1,234.3014	$1,234.30	$1,234.35	$1,234.30