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	$46.28	11.161%	$51.4453	$51.45	$51.45	$51.40
Purchase #2	$231.28	6.351%	$245.9686	$245.97	$245.95	$246.00
Purchase #3	$243.32	7.152%	$260.7222	$260.72	$260.70	$260.70
Purchase #4	$225.41	10.301%	$248.6295	$248.63	$248.65	$248.60
Purchase #5	$53.32	12.279%	$59.8672	$59.87	$59.85	$59.90
Purchase #6	$99.75	9.816%	$109.5415	$109.54	$109.55	$109.50
Purchase #7	$71.36	13.333%	$80.8744	$80.87	$80.85	$80.90
7 purchase totals =	$970.72		$1,057.0487	$1,057.05	$1,057.00	$1,057.00