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	$249.73	6.506%	$265.9774	$265.98	$266.00	$266.00
Purchase #2	$238.57	13.424%	$270.5956	$270.60	$270.60	$270.60
Purchase #3	$158.85	6.748%	$169.5692	$169.57	$169.55	$169.60
Purchase #4	$89.86	7.470%	$96.5725	$96.57	$96.55	$96.60
Purchase #5	$62.30	7.682%	$67.0859	$67.09	$67.10	$67.10
Purchase #6	$234.97	10.182%	$258.8946	$258.89	$258.90	$258.90
Purchase #7	$162.48	5.502%	$171.4196	$171.42	$171.40	$171.40
7 purchase totals =	$1,196.76		$1,300.1148	$1,300.12	$1,300.10	$1,300.20