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	$68.49	12.246%	$76.8773	$76.88	$76.90	$76.90
Purchase #2	$104.29	7.707%	$112.3276	$112.33	$112.35	$112.30
Purchase #3	$222.75	10.419%	$245.9583	$245.96	$245.95	$246.00
Purchase #4	$60.48	12.314%	$67.9275	$67.93	$67.95	$67.90
Purchase #5	$126.81	10.337%	$139.9183	$139.92	$139.90	$139.90
Purchase #6	$51.70	4.372%	$53.9603	$53.96	$53.95	$54.00
Purchase #7	$73.78	11.219%	$82.0574	$82.06	$82.05	$82.10
7 purchase totals =	$708.30		$779.0267	$779.04	$779.05	$779.10