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	$128.49	8.216%	$139.0467	$139.05	$139.05	$139.00
Purchase #2	$157.98	6.810%	$168.7384	$168.74	$168.75	$168.70
Purchase #3	$245.35	3.308%	$253.4662	$253.47	$253.45	$253.50
Purchase #4	$210.39	13.140%	$238.0352	$238.04	$238.05	$238.00
Purchase #5	$162.62	7.663%	$175.0816	$175.08	$175.10	$175.10
Purchase #6	$199.36	12.292%	$223.8653	$223.87	$223.85	$223.90
Purchase #7	$92.59	8.333%	$100.3055	$100.31	$100.30	$100.30
7 purchase totals =	$1,196.78		$1,298.5389	$1,298.56	$1,298.55	$1,298.50