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	$70.77	12.811%	$79.8363	$79.84	$79.85	$79.80
Purchase #2	$138.94	6.102%	$147.4181	$147.42	$147.40	$147.40
Purchase #3	$37.86	12.495%	$42.5906	$42.59	$42.60	$42.60
Purchase #4	$177.72	3.814%	$184.4982	$184.50	$184.50	$184.50
Purchase #5	$219.92	6.214%	$233.5858	$233.59	$233.60	$233.60
Purchase #6	$207.42	5.391%	$218.602	$218.60	$218.60	$218.60
Purchase #7	$178.94	9.855%	$196.5745	$196.57	$196.55	$196.60
7 purchase totals =	$1,031.57		$1,103.1055	$1,103.11	$1,103.10	$1,103.10