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	$37.28	12.397%	$41.9016	$41.90	$41.90	$41.90
Purchase #2	$19.97	6.676%	$21.3032	$21.30	$21.30	$21.30
Purchase #3	$166.28	10.642%	$183.9755	$183.98	$184.00	$184.00
Purchase #4	$94.39	4.631%	$98.7612	$98.76	$98.75	$98.80
Purchase #5	$99.96	9.524%	$109.4802	$109.48	$109.50	$109.50
Purchase #6	$78.99	4.518%	$82.5588	$82.56	$82.55	$82.60
Purchase #7	$208.63	5.593%	$220.2987	$220.30	$220.30	$220.30
7 purchase totals =	$705.50		$758.2792	$758.28	$758.30	$758.40