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	$108.34	13.587%	$123.0602	$123.06	$123.05	$123.10
Purchase #2	$74.36	5.614%	$78.5346	$78.53	$78.55	$78.50
Purchase #3	$216.59	12.521%	$243.7092	$243.71	$243.70	$243.70
Purchase #4	$160.90	9.359%	$175.9586	$175.96	$175.95	$176.00
Purchase #5	$108.47	5.471%	$114.4044	$114.40	$114.40	$114.40
Purchase #6	$13.48	13.187%	$15.2576	$15.26	$15.25	$15.30
Purchase #7	$129.40	7.842%	$139.5475	$139.55	$139.55	$139.50
7 purchase totals =	$811.54		$890.4721	$890.47	$890.45	$890.50