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	$192.54	11.870%	$215.3945	$215.39	$215.40	$215.40
Purchase #2	$96.36	8.705%	$104.7481	$104.75	$104.75	$104.70
Purchase #3	$116.36	10.222%	$128.2543	$128.25	$128.25	$128.30
Purchase #4	$189.63	10.514%	$209.5677	$209.57	$209.55	$209.60
Purchase #5	$135.37	13.368%	$153.4663	$153.47	$153.45	$153.50
Purchase #6	$81.54	10.172%	$89.8342	$89.83	$89.85	$89.80
Purchase #7	$81.49	8.467%	$88.3898	$88.39	$88.40	$88.40
7 purchase totals =	$893.29		$989.6549	$989.65	$989.65	$989.70