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	$78.34	10.116%	$86.2649	$86.26	$86.25	$86.30
Purchase #2	$180.84	4.451%	$188.8892	$188.89	$188.90	$188.90
Purchase #3	$14.31	10.580%	$15.824	$15.82	$15.80	$15.80
Purchase #4	$249.66	6.368%	$265.5583	$265.56	$265.55	$265.60
Purchase #5	$73.84	9.189%	$80.6252	$80.63	$80.65	$80.60
Purchase #6	$85.81	4.865%	$89.9847	$89.98	$90.00	$90.00
Purchase #7	$99.79	10.651%	$110.4186	$110.42	$110.40	$110.40
7 purchase totals =	$782.59		$837.5649	$837.56	$837.55	$837.60