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	$86.78	5.526%	$91.5755	$91.58	$91.60	$91.60
Purchase #2	$95.63	3.462%	$98.9407	$98.94	$98.95	$98.90
Purchase #3	$246.92	3.850%	$256.4264	$256.43	$256.45	$256.40
Purchase #4	$55.27	11.850%	$61.8195	$61.82	$61.80	$61.80
Purchase #5	$42.59	12.353%	$47.8511	$47.85	$47.85	$47.90
Purchase #6	$139.87	7.169%	$149.8973	$149.90	$149.90	$149.90
Purchase #7	$123.74	12.556%	$139.2768	$139.28	$139.30	$139.30
7 purchase totals =	$790.80		$845.7873	$845.80	$845.85	$845.80