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	$21.48	5.150%	$22.5862	$22.59	$22.60	$22.60
Purchase #2	$79.75	12.737%	$89.9078	$89.91	$89.90	$89.90
Purchase #3	$199.45	6.441%	$212.2966	$212.30	$212.30	$212.30
Purchase #4	$21.46	3.457%	$22.2019	$22.20	$22.20	$22.20
Purchase #5	$131.37	6.256%	$139.5885	$139.59	$139.60	$139.60
Purchase #6	$25.61	10.429%	$28.2809	$28.28	$28.30	$28.30
Purchase #7	$222.25	6.142%	$235.9006	$235.90	$235.90	$235.90
7 purchase totals =	$701.37		$750.7625	$750.77	$750.80	$750.80