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	$80.78	3.125%	$83.3044	$83.30	$83.30	$83.30
Purchase #2	$231.78	6.103%	$245.9255	$245.93	$245.95	$245.90
Purchase #3	$30.39	6.321%	$32.311	$32.31	$32.30	$32.30
Purchase #4	$223.51	6.357%	$237.7185	$237.72	$237.70	$237.70
Purchase #5	$244.32	6.449%	$260.0762	$260.08	$260.10	$260.10
Purchase #6	$156.76	7.661%	$168.7694	$168.77	$168.75	$168.80
Purchase #7	$60.46	12.372%	$67.9401	$67.94	$67.95	$67.90
7 purchase totals =	$1,028.00		$1,096.0451	$1,096.05	$1,096.05	$1,096.00