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	$73.89	6.148%	$78.4328	$78.43	$78.45	$78.40
Purchase #2	$78.73	4.738%	$82.4602	$82.46	$82.45	$82.50
Purchase #3	$110.74	11.495%	$123.4696	$123.47	$123.45	$123.50
Purchase #4	$109.27	4.854%	$114.574	$114.57	$114.55	$114.60
Purchase #5	$69.32	9.259%	$75.7383	$75.74	$75.75	$75.70
Purchase #6	$167.49	8.643%	$181.9662	$181.97	$181.95	$182.00
Purchase #7	$197.36	7.577%	$212.314	$212.31	$212.30	$212.30
7 purchase totals =	$806.80		$868.9551	$868.95	$868.90	$869.00